OFFSET
1,1
COMMENTS
Semiprimes s such that A062173(s) is also a semiprime.
LINKS
François Huppé, Table of n, a(n) for n = 1..10000
EXAMPLE
9 is in the sequence because 9 and (2^(9-1) mod 9)=4 are both semiprime.
MATHEMATICA
semiPrimeQ[x_] := Plus @@ Last /@ FactorInteger@ x == 2; fQ[n_] := semiPrimeQ@ n && semiPrimeQ@ PowerMod[2, n - 1, n]; Select[ Range@ 525, fQ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Dec 04 2010
STATUS
approved