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A141515 a(n) = phi(A067774(n)) where phi is Euler totient function. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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

MATHEMATICA

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

PROG

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

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

CROSSREFS

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

Sequence in context: A315732 A315733 A315734 * A315735 A315736 A315737

Adjacent sequences:  A141512 A141513 A141514 * A141516 A141517 A141518

KEYWORD

nonn

AUTHOR

Giovanni Teofilatto, Aug 11 2008

EXTENSIONS

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

STATUS

approved

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Last modified September 25 22:57 EDT 2018. Contains 315425 sequences. (Running on oeis4.)