Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #10 Sep 08 2022 08:45:35
%S 1,6,12,18,22,30,36,42,46,52,60,66,72,78,82,88,96,102,108,112,126,130,
%T 138,150,156,162,166,172,180,192,198,210,222,228,232,240,250,256,262,
%U 270,276,282,292,306,312,316,330,336,348,352,358,366,372,378,382,388
%N a(n) = phi(A067774(n)) where phi is Euler totient function.
%C Count of numbers smaller than and coprime to p for primes p such that p + 2 is composite.
%C Subsequence of A006093.
%H Vincenzo Librandi, <a href="/A141515/b141515.txt">Table of n, a(n) for n = 1..6970</a>
%t EulerPhi[#]&@Select[Prime@Range@80, !PrimeQ[# + 2] &] (* _Vincenzo Librandi_, Feb 09 2018 *)
%o (PARI) {forprime(p=2, 400, if(!isprime(p+2), print1(eulerphi(p), ",")))} \\ _Klaus Brockhaus_, Aug 31 2008
%o (Magma) [EulerPhi(p): p in PrimesUpTo(400) | not IsPrime(p+2)]; // _Vincenzo Librandi_, Feb 09 2018
%Y Cf A067774 (primes p such that p+2 is composite), A000010 (Euler totient function), A006093 (primes minus 1), A141426, A141427.
%K nonn
%O 1,2
%A _Giovanni Teofilatto_, Aug 11 2008
%E Edited and a(1) = 1, a(12) = 66 inserted by _Klaus Brockhaus_, Aug 31 2008