A283147 Number n such that there are no primes of the form sigma(n)/k where 1 < k < n is a (proper) nondivisor of n.

1, 2, 4, 9, 12, 16, 25, 48, 64, 112, 192, 240, 289, 448, 729, 960, 1344, 1681, 1984, 2401, 3481, 4096, 5041, 6720, 7921, 10201, 12288, 15625, 17161, 27889, 28561, 28672, 29929, 39270, 53130, 61440, 65536, 71610, 82110

Offset: 1

Author

Juri-Stepan Gerasimov, Mar 01 2017

Keywords

• nonn

Crossrefs

Supersequence of A023194, A019279 and A061652.

Cf. A000203, A173540.

Programs

PARI

is(n)=my(s=sigma(n), p=factor(s)[,1], k); for(i=1,#p, k=s/p[i]; if(kCharles R Greathouse IV, Mar 01 2017

Extensions

Corrected by Charles R Greathouse IV, Mar 01 2017