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Composite numbers c for which A000695(c) is prime.
2

%I #17 Dec 16 2018 06:40:51

%S 55,77,87,91,115,117,121,171,185,203,213,253,299,327,329,369,405,415,

%T 425,471,475,477,481,493,501,539,583,625,637,665,675,687,721,755,789,

%U 803,805,815,817,833,835,841,855,861,913,935,955,973,979,981

%N Composite numbers c for which A000695(c) is prime.

%t f[n_] := FromDigits[IntegerDigits[n, 2], 4]; Select[Range[1000], CompositeQ[#] && PrimeQ[f[#]] &] (* _Amiram Eldar_, Dec 13 2018 *)

%o (PARI) a000695(n) = fromdigits(binary(n), 4);

%o lista(nn) = forcomposite(n=1, nn, if (isprime(a000695(n)), print1(n, ", "))); \\ _Michel Marcus_, Dec 13 2018

%Y Cf. A000695, A077718, A152021, A152022, A152023, A152078, A152079.

%K nonn

%O 1,1

%A _Vladimir Shevelev_, Nov 23 2008

%E More terms derived from b000695.txt by _Michel Marcus_, Jun 02 2013