OFFSET
1,1
COMMENTS
If n is in A226961 then n is some product of elements of this sequence.
MATHEMATICA
fa = FactorInteger; free[n_] := n == Product[fa[n][[i, 1]], {i,
Length[fa[ n]]}]; Os[b_, 1] = True; Os[b_, 2] = True; Os[b_, b_] = True; Os[b_, n_] := Os[b, n] = PrimeQ[n] && free[(n-1)/ b^IntegerExponent[n - 1, b]] && IntegerExponent[n - 1, b] < 3 && Union@Table[Os[b, fa[n - 1][[i, 1]]], {i, Length[fa[n - 1]]}] == {True}; G[b_] := Select[Prime[Range[2000]], Os[b, #] &]; G[3]
CROSSREFS
KEYWORD
nonn
AUTHOR
José María Grau Ribas, Oct 05 2013
STATUS
approved