OFFSET
1,1
COMMENTS
For prime indices p such that p(p+1)/2 is even, see A002145 (Primes of form 4n+3).
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..5000
Eric Weisstein's World of Mathematics, Triangular Number
FORMULA
MATHEMATICA
Select[Table[Prime[n] (Prime[n] + 1)/2, {n, 500}], EvenQ[#] &] (* G. C. Greubel, Nov 03 2017 *)
PROG
(Python)
from sympy import primerange
def aupto(lim):
pitri = (p*(p+1)//2 for p in primerange(2, int((2*lim)**.5)+1))
return [t for t in pitri if t%2 == 0]
print(aupto(90000)) # Michael S. Branicky, Jun 28 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick De Geest, Oct 15 1998
STATUS
approved