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A143715
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Number of subsets {a,b,c} of {1,...,n} such that (a+b)^2+c^2 is a square (where c=max(a,b,c))
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2
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0, 0, 2, 3, 3, 6, 6, 10, 14, 14, 14, 25, 25, 25, 35, 43, 43, 50, 50, 67, 85, 85, 85, 113, 113, 113, 123, 139, 139, 158, 158, 173, 191, 191, 197, 230, 230, 230, 244, 286, 286, 321, 321, 337, 379, 379, 379, 456, 456, 456, 474, 493, 493, 512, 536, 589, 609, 609, 609
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OFFSET
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1,3
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COMMENTS
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Also: Number of cuboids of side lengths not exceeding n such that the shortest path over the surface from one vertex to the opposite one is integral (cf. link to Project Euler).
Also: partial sums of A143714, i.e., number of triples (a,b,c), 1 <= a <= b <= c <= n, such that (a+b)^2+c^2 is a square.
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LINKS
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M. F. Hasler, Table of n, a(n) for n=1,...,1000.
Project Euler: Problem 86
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FORMULA
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a(n) = sum( A143714(i), i=1..n ).
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EXAMPLE
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We have a(4) = a(5) = 3, corresponding to the cuboids of size 3 x 3 x 1, 3 x 2 x 2 and 4 x 2 x 1, i.e. to A143714(3)=2 and A143714(4)=1. No other cuboids with side lengths not exceeding 5 have the property that (a+b)^2+c^2 is a square. See A143714 for more details.
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PROG
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(PARI) A143715(M)=sum(a=1, M, sum(b=a, M, sum(c=b, M, issquare((a+b)^2+c^2))))
/* or: */ s=0; A143715=vector(100, i, s+=A143714[i])
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CROSSREFS
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Cf. A143714 (first differences).
Sequence in context: A222862 A101437 A039856 * A159685 A187763 A187262
Adjacent sequences: A143712 A143713 A143714 * A143716 A143717 A143718
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KEYWORD
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easy,nonn
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AUTHOR
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M. F. Hasler, Aug 29 2008, Aug 30 2008
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STATUS
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approved
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