A034954 Odd triangular numbers with prime indices.

3, 15, 91, 153, 435, 703, 861, 1431, 1891, 2701, 4005, 4753, 5151, 5995, 6441, 9453, 11175, 12403, 15051, 16471, 18721, 19503, 26335, 27261, 29161, 33153, 36315, 38503, 39621, 43071, 49141, 50403, 56953, 61075, 62481, 69751, 75855, 79003

Offset

1,1

Comments

For prime indices p such that p(p+1)/2 is 'odd' see A002313 (primes of form 4n+1).

Links

G. C. Greubel, Table of n, a(n) for n = 1..5000

Eric Weisstein's World of Mathematics, Triangular Number

Formula

a(n) = A000217(A002313(n)). - Michel Marcus, Nov 04 2017

Mathematica

Select[Table[Prime[n] (Prime[n] + 1)/2, {n, 500}], OddQ[#] &] (* G. C. Greubel, Nov 03 2017 *)
With[{nn=400}, Select[Thread[{Accumulate[Range[nn]], Range[nn]}], OddQ[ #[[1]]] && PrimeQ[#[[2]]]&]][[All, 1]] (* Harvey P. Dale, Mar 06 2019 *)

Crossrefs

Cf. A000217, A002313.

Cf. A014493, A034953, A034955.

Sequence in context: A024339 A319950 A336743 * A077783 A347319 A047019

Adjacent sequences: A034951 A034952 A034953 * A034955 A034956 A034957

Keyword

nonn

Author

Patrick De Geest, Oct 15 1998

Status

approved