A285791 Primes equal to a heptagonal number plus 1.

2, 19, 113, 149, 541, 617, 971, 1289, 1783, 2357, 3011, 3187, 5689, 6427, 7481, 7757, 9829, 12497, 12853, 14327, 15881, 17099, 18793, 21023, 24851, 28463, 30637, 31193, 45361, 50909, 54539, 60607, 63761, 66179, 69473, 70309, 83449, 88079, 90917, 91873, 94771

Offset

1,1

Links

Colin Barker, Table of n, a(n) for n = 1..1000

Prog

(PARI) pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number
maxk=300; L=List(); for(k=1, maxk, if(isprime(p=pg(7, k) + 1), listput(L, p))); Vec(L)
(Python)
from sympy import isprime
def heptagonal(n): return n*(5*n-3)//2
def aupto(limit):
  alst, n, hn = [], 1, heptagonal(1)
  while hn < limit:
    if isprime(hn+1): alst.append(hn+1)
    n, hn = n+1, heptagonal(n+1)
  return alst
print(aupto(94771)) # Michael S. Branicky, Feb 19 2021

Crossrefs

Cf. A000040, A000566, A002496, A055469, A285789, A285790, A285792.

Sequence in context: A396762 A240124 A278405 * A376481 A101253 A082291

Adjacent sequences: A285788 A285789 A285790 * A285792 A285793 A285794

Keyword

nonn

Author

Colin Barker, Apr 26 2017

Status

approved