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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A215462 Number of decompositions of 2n into ordered sums of two odd nonprimes.

Original entry on oeis.org

0, 1, 0, 0, 0, 2, 0, 0, 2, 1, 0, 2, 2, 2, 2, 3, 0, 4, 6, 0, 4, 5, 2, 4, 6, 5, 4, 7, 4, 6, 10, 2, 8, 11, 2, 9, 10, 6, 8, 13, 6, 8, 14, 8, 8, 17, 8, 10, 16, 7, 14, 17, 10, 12, 16, 11, 14, 19, 12, 12, 26, 10, 14, 25, 10, 19, 22, 16, 16, 21, 18, 20, 28, 18, 18, 31, 14, 23, 30, 16
Offset: 0

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Author

Peter A. Lawrence, Aug 11 2012

Keywords

Comments

A002372(n) + A215461(n) + a(n) = n.
Note: if n is odd-composite then a(n) is odd, otherwise even.
Conjecture: a(n) is never zero for n > 19, verified to 10^9.
Conjecture: a(n) > A215461(n) > A002372(n) for sufficiently large n.

Examples

			n=15, 2*n=30, 2*n = { 9+21, 15+15, 21+9 }, a(15) = 3.
n=18, 2*n=36, 2*n = { 1+35, 9+27, 15+21, 21+15, 27+9, 35+1 }, a(18) = 6.

Crossrefs

Cf. A002372, A215461.

Formula

a(n) = convolve(c,c) where c(n) is the sequence defined by 1 if (2*n+1) is odd nonprime (includes 1), and 0 if (2*n+1) is odd prime.
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