OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..10000

EXAMPLE

(6*141)-1 = 845, which has >2 prime factors (counted with multiplicity), namely 5,13 and 13. (6*141)+1 = 847, which has >2 prime factors (counted with multiplicity), namely 7,11 and 11. So 141 is in the sequence.

MATHEMATICA

For[x = 6, x < 10001, x += 6, If[PrimeQ[x - 1] == True, y = "P", S = 0; F = FactorInteger[x - 1]; For[k = 1, k < Length[F] + 1, k++, S += F[[k]][[2]]]; If[S == 2, y = "A", y = "N"]]; If[PrimeQ[x + 1] == True, z = "P", S = 0; F = FactorInteger[x + 1]; For[k = 1, k < Length[F] + 1, k++, S += F[[k]][[2]]]; If[S == 2, z = "A", z = "N"]]; If[y == "N" && z == "N", Print[x/6]]]

Select[Range[2000], PrimeOmega[6#+1]>2&&PrimeOmega[6#-1]>2&] (* Harvey P. Dale, Apr 26 2016 *)

CROSSREFS

KEYWORD

nonn

AUTHOR

Arran Fernandez, Oct 03 2008

STATUS

approved