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A201786 Primes of the form 5*k^2 - 4. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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

MATHEMATICA

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

PROG

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

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

CROSSREFS

Cf. A090562, A195317.

Sequence in context: A142392 A142943 A142183 * A167443 A098675 A056213

Adjacent sequences:  A201783 A201784 A201785 * A201787 A201788 A201789

KEYWORD

nonn

AUTHOR

Vincenzo Librandi, Dec 05 2011

STATUS

approved

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Last modified July 5 23:36 EDT 2020. Contains 335475 sequences. (Running on oeis4.)