A171569 - OEIS

A171569

Triangular numbers T such that T-2 is a prime.

15, 21, 45, 55, 91, 105, 153, 231, 253, 351, 435, 465, 595, 703, 741, 861, 1035, 1225, 1431, 1485, 1711, 1891, 1953, 2145, 2701, 3003, 3081, 3321, 3741, 4005, 4095, 4465, 4753, 5565, 5671, 6555, 7021, 7875, 8515, 9045, 10011, 10153, 10731, 11175, 11781

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..45.

EXAMPLE

15-2 = 13, 21-2 = 19, 45-2 = 43, ...

MATHEMATICA

Select[s=0; Table[n*(n+1)/2, {n, 6!}], PrimeQ[ #-2]&]

Select[Accumulate[Range[200]], PrimeQ[#-2]&] (* Harvey P. Dale, Apr 09 2018 *)

CROSSREFS

Cf. A000217, A129545, A129752.