A049511 Numbers k such that prime(k) == 1 (mod 10).

5, 11, 13, 18, 20, 26, 32, 36, 42, 43, 47, 53, 54, 58, 60, 64, 67, 79, 82, 83, 89, 94, 98, 100, 105, 110, 115, 116, 121, 125, 126, 133, 135, 141, 142, 152, 156, 160, 164, 167, 172, 173, 177, 178, 182, 190, 193, 194, 197, 202, 210, 212, 216, 218, 221, 230, 233

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Also k for which prime(k) == 1 (mod 5). - Bruno Berselli, Mar 04 2016

The asymptotic density of this sequence is 1/4 (by Dirichlet's theorem). - Amiram Eldar, Mar 01 2021

Links

• Zak Seidov, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000720, A024912, A030430, A081759.

Cf. A049508, A049509, A049510.

Programs

Mathematica

Select[Range[210], Mod[Prime[ # ], 10] == 1 &] (* Ray Chandler, Nov 07 2006 *)

PARI

isok(n) = !((prime(n)-1) % 10); \\ Michel Marcus, Mar 04 2016

Sage

[n for n in (1..300) if Mod(nth_prime(n), 10) == 1] # Bruno Berselli, Mar 04 2016

Formula

a(n) = A000720(A030430(n)). - Ray Chandler, Nov 07 2006

Extensions

Extended by Ray Chandler, Nov 28 2003

Formula corrected by Zak Seidov, Sep 20 2011