@@ -12,6 +12,7 @@ If we list all the natural numbers below $10$ that are multiples of $3$ or $5$,
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Suppose the base numbers were $2$ and $3$ below $10$ so $9$, they would create duplicates, ie $6$ is counted twice. Therefore take the sum of each multiple to the limit, and one time remove the numbers counted twice:
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Suppose the base numbers were $2$ and $3$ below $10$ so $9$, they would create duplicates, ie $6$ is counted twice. Therefore take the sum of each multiple to the limit, and one time remove the numbers counted twice:
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#html.frame(
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$
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$
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&2+4+6+8+3+cancel(6)+9 = 32\
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&2+4+6+8+3+cancel(6)+9 = 32\
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&sum_(i=1)^(floor(9/(2)))2i + sum_(i=1)^(floor(9/(3))) 3i - sum_(i=1)^(floor(9/(6))) 6i \
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&sum_(i=1)^(floor(9/(2)))2i + sum_(i=1)^(floor(9/(3))) 3i - sum_(i=1)^(floor(9/(6))) 6i \
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@@ -20,15 +21,17 @@ $
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= 2& (4(5))/2 + 3 (3(4))/2 - 6 (1(2))/2\
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= 2& (4(5))/2 + 3 (3(4))/2 - 6 (1(2))/2\
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= 3&2
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= 3&2
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$
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$
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)
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This revealed a general solution, for base numbers $n, m$ below $L$:
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This revealed a general solution, for base numbers $n, m$ below $L$:
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#html.frame(
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$
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$
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f(n,m,L) =&n sum_(i=1)^floor((L-1)/n) i + m sum_(i=1)^floor((L-1)/m) i- n m sum_(i=1)^floor((L-1)/(n m))i \
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f(n,m,L) =&n sum_(i=1)^floor((L-1)/n) i + m sum_(i=1)^floor((L-1)/m) i- n m sum_(i=1)^floor((L-1)/(n m))i \
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"Define "&a = floor((L-1)/n), b = floor((L-1)/m), c = floor((L-1)/(n m)) \
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"Define "&a = floor((L-1)/n), b = floor((L-1)/m), c = floor((L-1)/(n m)) \
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=> f(n,m,L) =& (n a(a+1) + m b(b+1) - n m (c)(c+1))/2
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=> f(n,m,L) =& (n a(a+1) + m b(b+1) - n m (c)(c+1))/2
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$
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$
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)
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Testing this as code:
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Testing this as code:
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```py
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```py
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@@ -61,6 +64,8 @@ The goal is to not add the number if it was already added.
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Mathamatically this can be done piecewise. If a previous element of $A$ divides $A_i k$, skip that number.
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Mathamatically this can be done piecewise. If a previous element of $A$ divides $A_i k$, skip that number.
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#html.frame(
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$
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$
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f(A, L) = sum_(i)^abs(A)[sum_(k=1)^floor((L-1)/A_i) cases(0 quad & A_j divides A_i k and j < k, A_i k quad & A_j divides.not A_i k and j < k)]
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f(A, L) = sum_(i)^abs(A)[sum_(k=1)^floor((L-1)/A_i) cases(0 quad & A_j divides A_i k and j < k, A_i k quad & A_j divides.not A_i k and j < k)]
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$
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$
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)
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Reference in New Issue
Block a user