1,1

Semiprimes n such that A062173(n) is also a semiprime.

Table of n, a(n) for n=1..53.

9 is in the sequence because 9 and (2^(9-1) mod 9)=4 are both semiprime.

semiPrimeQ[x_] := Plus @@ Last /@ FactorInteger@ x == 2; fQ[n_] := semiPrimeQ@ n && semiPrimeQ@ PowerMod[2, n - 1, n]; Select[ Range@ 525, fQ]

Cf. A001358, A062173, A175168.

Sequence in context: A331662 A007962 A061254 * A096788 A050991 A033553

Adjacent sequences: A175623 A175624 A175625 * A175627 A175628 A175629

nonn

Juri-Stepan Gerasimov, Dec 04 2010

approved