A141515 a(n) = phi(A067774(n)) where phi is Euler totient function.

1, 6, 12, 18, 22, 30, 36, 42, 46, 52, 60, 66, 72, 78, 82, 88, 96, 102, 108, 112, 126, 130, 138, 150, 156, 162, 166, 172, 180, 192, 198, 210, 222, 228, 232, 240, 250, 256, 262, 270, 276, 282, 292, 306, 312, 316, 330, 336, 348, 352, 358, 366, 372, 378, 382, 388

Offset: 1

Author

Giovanni Teofilatto, Aug 11 2008

Keywords

• nonn

Comments

Count of numbers smaller than and coprime to p for primes p such that p + 2 is composite.

Subsequence of A006093.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..6970

Crossrefs

Cf A067774 (primes p such that p+2 is composite), A000010 (Euler totient function), A006093 (primes minus 1), A141426, A141427.

Programs

Magma

[EulerPhi(p): p in PrimesUpTo(400) | not IsPrime(p+2)]; // Vincenzo Librandi, Feb 09 2018

Mathematica

EulerPhi[#]&@Select[Prime@Range@80, !PrimeQ[# + 2] &] (* Vincenzo Librandi, Feb 09 2018 *)

PARI

{forprime(p=2, 400, if(!isprime(p+2), print1(eulerphi(p), ",")))} \\ Klaus Brockhaus, Aug 31 2008

Extensions

Edited and a(1) = 1, a(12) = 66 inserted by Klaus Brockhaus, Aug 31 2008