A153275 Numbers n such that 10*n+1 is not prime.

0, 2, 5, 8, 9, 11, 12, 14, 16, 17, 20, 22, 23, 26, 29, 30, 32, 34, 35, 36, 37, 38, 39, 41, 44, 45, 47, 48, 50, 51, 53, 55, 56, 58, 59, 61, 62, 65, 67, 68, 71, 72, 73, 74, 77, 78, 79, 80, 83, 84, 85, 86, 87, 89, 90, 92, 93, 95, 96, 98, 100, 101, 104, 107, 108, 110

Offset: 1

Author

Vincenzo Librandi, Dec 22 2008

Keywords

• nonn
• easy

Comments

Multiplied by 2 we have 4,10,16,18,... which is the set of even terms of A153329. - R. J. Mathar, Jan 23 2009

Examples

			Distribution of the terms in the following triangular array:
*;
*,*;
2,*,*;
*,*,*,8;
*,*,*,*,12;
*,*,9,*,*,*;
*,*,*,*,*,*,*;
5,*,*,*,*,22,*,*;
*,*,*,17,*,*,*,*,36;
*,*,*,*,23,*,*,*,*,44;
*,*,16,*,*,*,*,39,*,*,*; etc.
where * marks the non-integer values of (2*h*k + k + h)/5 with h >= k >= 1. - _Vincenzo Librandi_, Jan 15 2013
		

Links

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

Crossrefs

Cf. A024912, A053178, A153329.

Programs

Magma

[n: n in [0..150] | not IsPrime(10*n + 1)]; // Vincenzo Librandi, Jan 12 2013

Maple

q:= n-> not isprime(10*n+1):
select(q, [$0..120])[];  # Alois P. Heinz, Jan 21 2021

Mathematica

Select[Range[0, 200], !PrimeQ[10*# + 1]&] (* Vincenzo Librandi, Jan 12 2013 *)

Formula

a(n) = (A053178(n)-1)/10. - R. J. Mathar, Oct 30 2009

Extensions

63 replaced by 53 by R. J. Mathar, Jan 23 2009

0 added by Arkadiusz Wesolowski, Aug 03 2011