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A309009 Numbers that are both triangular and octahedral. 1
0, 1, 6, 231 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

The list is probably finite, like the list of triangular and tetrahedral numbers (A027568).

It would appear that the similar sequence of pentagonal-dodecahedral numbers contains only the trivial cases 0 and 1.

Intersection of A000217 and A005900. - A.H.M. Smeets, Aug 19 2019

LINKS

Table of n, a(n) for n=1..4.

MATHEMATICA

triQ[n_] := IntegerQ[Sqrt[8n + 1]]; oct[n_] := n(2n^2 + 1)/3 ; Select[oct@Range[0, 10], triQ] (* Amiram Eldar, Jul 15 2019 *)

PROG

(PARI) lista(nn) = for (n=0, nn, if (ispolygonal(k=n*(2*n^2 + 1)/3, 3), print1(k, ", "))); \\ Michel Marcus, Jul 06 2019

CROSSREFS

Cf. A000217, A005900, A027568, A307174.

Sequence in context: A282736 A277293 A177043 * A117064 A112001 A286314

Adjacent sequences:  A309006 A309007 A309008 * A309010 A309011 A309012

KEYWORD

nonn,fini,more

AUTHOR

William C. Laursen, Jul 05 2019

STATUS

approved

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Last modified October 28 16:09 EDT 2021. Contains 348329 sequences. (Running on oeis4.)