A140390 Nonprimes of the form 21k+1.

1, 22, 64, 85, 106, 148, 169, 190, 232, 253, 274, 295, 316, 358, 400, 442, 484, 505, 526, 568, 589, 610, 652, 694, 715, 736, 778, 799, 820, 841, 862, 904, 925, 946, 988, 1030, 1072, 1114, 1135, 1156, 1177, 1198, 1219, 1240, 1261, 1282, 1324

Offset: 1

Author

Juri-Stepan Gerasimov, Jun 12 2008

Keywords

• nonn
• less

Comments

The prime numbers 421=20*21+1 and 673=32*21+1, for example, are neither in here nor in A136069.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A136069.

Programs

Magma

[a: n in [0..90] | not IsPrime(a) where a is 21*n+1]; // Vincenzo Librandi, Mar 22 2014

Mathematica

Select[21 Range[0, 100] + 1, ! PrimeQ@# &] (* Vincenzo Librandi, Mar 22 2014 *)

Extensions

Edited by R. J. Mathar, Jun 17 2008