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A124198 Numbers k such that 21*k + 1 is prime. 2
2, 6, 10, 16, 18, 20, 22, 26, 30, 32, 36, 42, 46, 48, 50, 52, 62, 68, 70, 76, 82, 92, 96, 102, 108, 110, 116, 120, 126, 128, 130, 136, 146, 148, 158, 160, 168, 170, 172, 176, 178, 182, 186, 198, 200, 202, 206, 220, 222, 228, 230, 236, 238, 246, 248, 258, 262, 278 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

If k=148 then 21*k + 1 = 3109 (prime).

MATHEMATICA

Select[Range[300], PrimeQ[21#+1]&] (* Harvey P. Dale, Mar 08 2016 *)

PROG

(MAGMA) [n: n in [0..300] | IsPrime(21*n + 1)] // Vincenzo Librandi, Mar 26 2010

(PARI) is(n)=isprime(21*n+1) \\ Charles R Greathouse IV, Jun 06 2017

CROSSREFS

Cf. A024905, A124127.

Sequence in context: A293408 A097022 A137236 * A032426 A220453 A195957

Adjacent sequences:  A124195 A124196 A124197 * A124199 A124200 A124201

KEYWORD

nonn,easy

AUTHOR

Parthasarathy Nambi, Dec 06 2006

STATUS

approved

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Last modified February 24 17:29 EST 2020. Contains 332209 sequences. (Running on oeis4.)