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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
OFFSET
1,2
COMMENTS
a(n+1) is the (n+2)-th odd sum of two consecutive nonnegative nonprimes.
LINKS
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
KEYWORD
nonn
AUTHOR
EXTENSIONS
Entries checked by R. J. Mathar, Apr 20 2010
STATUS
approved