1,5

It appears that a(n)= 0 if and only if n divides 24 (See also the comments in A018253).

Table of n, a(n) for n=1..90.

Omar E. Pol, Determinacion geometrica de los numeros primos y perfectos

Omar E. Pol, Illustration: Divisors and pi(x)

a(n) = 2*(A000196(n) - A038548(n)) = 2*A236627(n). - Omar E. Pol, Feb 05 2014

Cf. A000005, A000720, A018253, A160811, A161205.

Sequence in context: A140302 A085341 A221474 * A176866 A294614 A063918

Adjacent sequences: A160809 A160810 A160811 * A160813 A160814 A160815

easy,nonn

Omar E. Pol, Jun 19 2009

Edited by Omar E. Pol, Aug 02 2009

approved