A201786 Primes of the form 5*k^2 - 4.

41, 241, 401, 601, 1801, 3121, 4201, 4801, 5441, 6121, 6841, 9241, 13001, 15121, 17401, 19841, 21121, 22441, 23801, 26641, 29641, 32801, 45121, 47041, 51001, 57241, 63841, 75641, 78121, 91121, 96601, 99401, 102241, 108041, 114001, 117041

Offset: 1

Author

Vincenzo Librandi, Dec 05 2011

Keywords

• nonn

Comments

Also, primes of the form 20*k^2 + 20*k + 1. - Jan Rider, May 22 2018

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..5000

Crossrefs

Cf. A090562, A195317.

Programs

Magma

[a: n in [1..400] | IsPrime(a) where a is 5*n^2-4];

Mathematica

Select[Table[5n^2-4,{n,1,1000}],PrimeQ]

PARI

lista(nn) = for (n=1, nn, if (isprime(p=5*n^2-4), print1(p, ", "));); \\ Michel Marcus, May 22 2018