A257772 Numbers n>=0 such that (n+1)^3 - n^3 = 3*n^2+3*n+1 is not prime.

0, 5, 7, 8, 12, 15, 16, 18, 19, 20, 21, 22, 26, 29, 31, 33, 35, 36, 39, 40, 43, 44, 46, 47, 50, 51, 53, 54, 56, 57, 59, 60, 61, 64, 65, 68, 69, 70, 71, 72, 73, 75, 76, 77, 78, 79, 82, 83, 84, 85, 87, 89, 92, 94, 96, 97, 98, 99, 100, 101, 102, 103, 104, 106

Offset: 1

Author

Miguel Angel Velilla Mula, May 08 2015

Keywords

• nonn
• easy

Comments

Complement of A111251.

Includes all members of A047383 except 1. - Robert Israel, May 12 2015

Examples

			5 is a term since (5+1)^3 - 5^3 = 91 = 13*7 is not prime.
		

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003215, A047383, A111251.

Programs

Magma

[n: n in [0..120] | not IsPrime(3*n^2+3*n+1)]; // Vincenzo Librandi, May 13 2015

Maple

remove(t -> isprime((t+1)^3-t^3), [$0..300]); # Robert Israel, May 12 2015

Mathematica

Select[Range[0, 200], ! PrimeQ[(#+1)^3 - #^3] &] (* Giovanni Resta, May 08 2015 *)

PARI

for(n=0,100,if(!isprime(3*n^2+3*n+1),print1(n,", "))) \\ Derek Orr, May 19 2015

UBASIC

10 print 0
20 for n=1 to 200
30   s = (n+1)^3 - n^3
40   if prmdiv(s)<>s then print n
50 next n

Formula

a(n) ~ n. - Charles R Greathouse IV, May 22 2015