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A228428 Number of ways to write n = x + y (x, y > 0) with p(99, x) + p(100, y) prime, where p(m, k) denotes the m-gonal number (m-2)*k*(k-1)/2 + k. 6
0, 1, 1, 1, 2, 1, 1, 1, 3, 3, 1, 2, 4, 1, 3, 5, 4, 3, 5, 1, 4, 3, 2, 1, 7, 5, 1, 4, 4, 4, 4, 5, 2, 5, 4, 2, 6, 1, 4, 9, 6, 4, 6, 6, 5, 6, 5, 4, 6, 5, 11, 9, 6, 5, 10, 4, 3, 9, 5, 3, 11, 7, 7, 10, 5, 5, 10, 5, 5, 5, 4, 7, 6, 6, 5, 13, 7, 3, 12, 5, 5, 12, 6, 7, 8, 6, 4, 9, 7, 8, 9, 10, 9, 9, 8, 15, 17, 9, 9, 10 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

COMMENTS

Conjecture: a(n) > 0 for all n > 1.

See also A228425 for other similar conjectures.

LINKS

Zhi-Wei Sun, Table of n, a(n) for n = 1..10000

Zhi-Wei Sun, On universal sums of polygonal numbers, preprint, arXiv:0905.0635.

EXAMPLE

a(8) = 1 since 8 = 3 + 5 with p(99, 3) + p (100, 5) = 1279 prime.

a(38) = 1 since 38 = 6 + 32 with p(99, 6) + p(100, 32) = 50101 prime.

MATHEMATICA

p[m_, x_]:=(m-2)x(x-1)/2+x

a[n_]:=Sum[If[PrimeQ[p[99, x]+p[100, n-x]], 1, 0], {x, 1, n-1}]

Table[a[n], {n, 1, 100}]

CROSSREFS

Cf. A000040, A228425.

Sequence in context: A239062 A201160 A302538 * A321915 A321748 A263447

Adjacent sequences:  A228425 A228426 A228427 * A228429 A228430 A228431

KEYWORD

nonn

AUTHOR

Zhi-Wei Sun, Nov 10 2013

STATUS

approved

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Last modified September 19 04:52 EDT 2019. Contains 327187 sequences. (Running on oeis4.)