A073411 cototient(x) - 1 where x are the odd semiprimes (i.e., x are odd terms in A001358).

2, 6, 8, 4, 12, 10, 14, 6, 18, 14, 20, 16, 24, 16, 20, 30, 18, 32, 22, 38, 26, 22, 10, 42, 44, 24, 48, 22, 32, 34, 54, 28, 12, 60, 62, 40, 26, 68, 34, 44, 28, 72, 46, 36, 74, 28, 50, 80, 30, 84, 32, 42, 56, 90, 46, 16, 98, 62, 34, 48, 102, 64, 104, 38, 108, 34, 110, 52, 70

Offset: 1

Author

Benoit Cloitre, Aug 23 2002

Keywords

• easy
• nonn

Comments

If the Goldbach conjecture is true, all even numbers appear at least once in the sequence since pq - phi(pq) - 1 = p + q.

Links

• Michael De Vlieger, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001358 (semiprimes), A046315 (odd semiprimes), A051953 (cototient).

Programs

Mathematica

Map[# - EulerPhi@ # - 1 &, Select[Range[1, 335, 2], PrimeOmega # == 2 &]] (* Michael De Vlieger, Jul 30 2017 *)

PARI

lista(nn) = forstep(n=1, nn, 2, if (bigomega(n)==2, print1(n-eulerphi(n)-1, ", "))); \\ Michel Marcus, Jul 30 2017

Formula

a(n) = A051953(A046315(n)) - 1. - Michel Marcus, Jul 30 2017; corrected Dec 29 2020