0,2

Table of n, a(n) for n=0..60.

30 is in the sequence because 30-phi(30)=22, which is a pentagonal number.

(PARI) isok(n) = ispolygonal(n - eulerphi(n), 5); \\ Michel Marcus, Feb 26 2014

Cf. A000326, A051953.

Sequence in context: A171049 A171053 A171055 * A100546 A117094 A171057

Adjacent sequences: A117282 A117283 A117284 * A117286 A117287 A117288

nonn

Luc Stevens (lms022(AT)yahoo.com), Apr 23 2006

approved