A107816 a(n) = sigma(A067651(n)).

1, 8, 20, 48, 144, 240, 720, 480, 756, 720, 864, 2304, 2880, 4080, 5040, 6240, 6048, 6720, 9984, 21600, 90720, 506880, 806400, 748800, 973440, 1153152

Offset

1,2

Comments

Numbers n such that n = sigma(k) = phi(prime(k)-1) for some k.

Values of k are in A067651, values of prime(k) are in A107815.

Links

Table of n, a(n) for n=1..26.

Example

a(3) = sigma(A067651(3)) = sigma(19) = 20.

Prog

(PARI) m=400000; for(n=1, m, s=sigma(n); if(s==eulerphi(prime(n)-1), print1(s, ", ")))

Crossrefs

Cf. A067651, A107815.

Sequence in context: A273266 A273304 A169878 * A361073 A361215 A205219

Adjacent sequences: A107813 A107814 A107815 * A107817 A107818 A107819

Keyword

nonn,more

Author

Klaus Brockhaus, May 24 2005

Status

approved