A176462 Numbers k such that neither k-1 nor k+1 is prime or semiprime.

0, 17, 19, 29, 31, 41, 43, 49, 51, 53, 55, 65, 67, 69, 71, 77, 79, 89, 91, 97, 99, 101, 103, 109, 111, 113, 115, 125, 127, 129, 131, 137, 139, 149, 151, 153, 155, 161, 163, 169, 171, 173, 175, 181, 183, 185, 187, 189, 191, 197, 199, 209, 211, 221, 223, 229, 231

Offset

1,2

Comments

a(n+1) is the (n+2)-th odd sum of two consecutive nonnegative nonprimes.

Links

Harvey P. Dale, Table of n, a(n) for n = 1..2000

Formula

a(n+1) = A166685(n+2).

Example

0 is a term because neither 0-1=-1 nor 0+1=1 is prime or semiprime.

Maple

isA001358 := proc(n) numtheory[bigomega](n) = 2 ; end proc: for n from 0 to 400 do if isA001358(n+1) or isA001358(n-1) or isprime(n+1) or isprime(n-1) then ; else printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 20 2010

Mathematica

Join[{0}, Flatten[Position[Partition[Table[If[PrimeQ[n]||PrimeOmega[n] == 2, 1, 0], {n, 250}], 3, 1], _?(#[[1]]==#[[3]]==0&), {1}, Heads -> False]]+ 1] (* Harvey P. Dale, Oct 27 2015 *)

Crossrefs

Cf. A141468.

Sequence in context: A096990 A175384 A053689 * A060254 A190792 A137796

Adjacent sequences: A176459 A176460 A176461 * A176463 A176464 A176465

Keyword

nonn

Author

Juri-Stepan Gerasimov, Apr 18 2010

Extensions

Entries checked by R. J. Mathar, Apr 20 2010

Status

approved