A333015 Numbers which can be written in exactly five ways as a sum of two distinct nonzero pentagonal numbers.

205427, 210552, 230102, 269712, 333802, 346977, 354537, 384802, 397892, 416677, 420077, 426622, 448552, 470902, 471927, 478302, 509752, 520852, 563772, 566177, 569507, 571377, 575202, 580302, 586102, 590162, 599847, 610052, 616552, 618263, 635552, 646177, 647947

Offset

1,1

Links

Table of n, a(n) for n=1..33.

Example

205427 = P(234) + P(287) = P(201) + P(311) = P(166) + P(331) = P(56) + P(366) = P(49) + P(367), where P(n) is the n-th pentagonal number (A000326).

Prog

(PARI) is(k) = sum(i=1, sqrt(1+12*k)\6, sqrt(1+24*k+12*i-36*i*i)%6==5) == 5; \\ Jinyuan Wang, Mar 06 2020

Crossrefs

Cf. A000326, A332988, A332989, A333011, A333012, A333013, A333014.

Sequence in context: A218448 A234836 A206093 * A177006 A236033 A234068

Adjacent sequences: A333012 A333013 A333014 * A333016 A333017 A333018

Keyword

nonn

Author

Olivier Gérard, Mar 05 2020

Extensions

More terms from Jinyuan Wang, Mar 06 2020

Status

approved