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A224421
The indices of tetrahedral numbers that are also triangular.
2
0, 1, 3, 8, 20, 34
OFFSET
0,3
LINKS
E. T. Avanesov, Solution of a problem on figurate numbers (in Russian), Acta Arith. 12 1966/1967 pages 409-420.
EXAMPLE
The eighth tetrahedral number is 120, which is also a triangular number. Hence, 8 belongs to the sequence.
MATHEMATICA
Select[Table[{n, (n(n+1)(n+2))/6}, {n, 0, 35}], OddQ[Sqrt[1+8#[[2]]]]&][[;; , 1]] (* Harvey P. Dale, May 31 2024 *)
PROG
(PARI) for(n=0, 34, if(ispolygonal(n*(n+1)*(n+2)/6, 3), print1(n", "))) \\ Charles R Greathouse IV, Apr 07 2013
CROSSREFS
Sequence in context: A195676 A027299 A321067 * A354317 A143785 A182735
KEYWORD
nonn,full,fini
AUTHOR
Tanya Khovanova, Apr 06 2013
STATUS
approved