1,1

a(13) > 10^11.

Table of n, a(n) for n=1..12.

The divisors of 10 smaller than 10 are 1, 2 and 5. Since sigma(1) + sigma(2) + sigma(5) = 10, 10 is in the sequence.

Select[Range[2, 120000], Mod[Total@DivisorSigma[1, Most@Divisors@#], #] == 0 &]

Cf. A221219.

Sequence in context: A222367 A220817 A114918 * A149213 A149214 A149215

Adjacent sequences: A224485 A224486 A224487 * A224489 A224490 A224491

nonn

Giovanni Resta, Apr 08 2013

a(9)-a(12) and bound on a(13) from Donovan Johnson.

approved