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A176462 Numbers k such that neither k-1 nor k+1 is prime or semiprime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 29 21:32 EST 2021. Contains 349416 sequences. (Running on oeis4.)