A175915 Odd terms of A109510.

2205, 312896925, 1874196225, 3356107425, 4181881725, 4987853325, 6946213725, 8860349025, 13250605725, 17989980525, 25443641025, 32177090925, 38286871425, 55531730925, 75756402225, 113679103725, 152738872209, 170812073025, 179835853725, 186091427025

Offset: 1

Author

Zak Seidov, Oct 15 2010

Keywords

• nonn

Comments

a(1)=2205=A109510(29), a(2)-a(8) from Max Alekseyev.

sqrt(sigma(a(n))-2*a(n)): 6, 3432, 8250, 11022, 19376.

Crossrefs

Cf. A109510 sigma(n)-2n is a square.

Programs

PARI

is(n)=n%2&&issquare(sigma(n)-2*n) \\ Charles R Greathouse IV, Dec 06 2011

Extensions

a(6)-a(18) from Donovan Johnson, Oct 17 2010

a(19)-a(20) from Donovan Johnson, Dec 06 2011