A396641 Centered hexagonal numbers h such that 7*h is also a centered hexagonal number.

1, 217, 55081, 13990321, 3553486417, 902571559561, 229249622642041, 58228501579518817, 14789810151575137441, 3756553549998505391161, 954149811889468794217417, 242350295666375075225832721, 61556020949447379638567293681, 15634986970863968053120866762217, 3971225134578498438113061590309401

Offset

1,2

Links

Steven Lu, Table of n, a(n) for n = 1..416

Formula

a(n) = (6*A253880(n) + 1) / 7.

Example

217 is in this sequence since both 217 and 217*7=1519 are centered hexagonal numbers.

Mathematica

(6 NestList[({{0, 1}, {-1, 254}}.#) &, {1, 253}, 14][[;; , 1]] + 1)/7

Crossrefs

Cf. A003215, A253880.

Sequence in context: A086026 A375816 A100794 * A048258 A373762 A013541

Adjacent sequences: A396638 A396639 A396640 * A396642 A396643 A396644

Keyword

nonn,easy

Author

Steven Lu, May 31 2026

Status

approved