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

1,2

Comments

Complement of A111251.

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

Links

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

Formula

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

Example

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

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 *)

Prog

(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
(Magma) [n: n in [0..120] | not IsPrime(3*n^2+3*n+1)]; // Vincenzo Librandi, May 13 2015
(PARI) for(n=0, 100, if(!isprime(3*n^2+3*n+1), print1(n, ", "))) \\ Derek Orr, May 19 2015

Crossrefs

Cf. A003215, A047383, A111251.

Sequence in context: A173664 A171420 A047384 * A356897 A314374 A066001

Adjacent sequences: A257769 A257770 A257771 * A257773 A257774 A257775

Keyword

nonn,easy

Author

Miguel Angel Velilla Mula, May 08 2015

Status

approved