A173013 a(1) = 1, for n >= 2; a(n) = the smallest number h such that sigma(h) = A000203(h) = a(n-1) + 3, a(n) = 0 if no such number exists.

1, 3, 5, 7, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2

Offset: 1

Author

Jaroslav Krizek, Nov 06 2010

Keywords

• nonn
• easy

Comments

a(n) is eventually periodic sequence with period (0, 2).

Crossrefs

Cf. A000035, A173012, A173014, A173015, A173016.

Programs

PARI

a(n)=if(n>4,2-n%2*2,2*n-1) \\ Charles R Greathouse IV, Feb 14 2013

Formula

A000203(a(n)) = a(n-1) + 3 for n >= 2.