A228434 Primes expressible as sigma(n) + sigma(sigma(n)), in order of their occurrence.

2, 7, 11, 23, 127, 167, 137, 269, 547, 547, 383, 547, 269, 431, 547, 547, 293, 383, 431, 1171, 1039, 1171, 641, 1039, 1103, 1171, 887, 1361, 2551, 1861, 3001, 2753, 1193, 2963, 1499, 2153, 2753, 2551, 2963, 4327, 5281, 1823, 2963, 4219, 4327, 3593, 3583, 6763

Offset

1,1

Links

K. D. Bajpai, Table of n, a(n) for n = 1..2450

Example

a(6)= 167: sigma(32)+sigma(sigma(32))= 63+104= 167, which is prime.
a(11)= 383: sigma(93)+sigma(sigma(93))= 128+255= 383, which is prime.

Maple

with(numtheory):KD := proc() local a; a:= sigma(n)+sigma(sigma(n)); if isprime(a) then RETURN (a); fi; end:seq(KD(), n=1..5000);

Crossrefs

Cf. A000203 (sigma(n): sum of divisors of n).

Cf. A019279 (superperfect numbers: sigma(sigma(n))).

Cf. A033632 (numbers n: sigma(n)is prime).

Cf. A051027 (a(n)= sigma(sigma(n))).

Sequence in context: A179876 A088179 A362629 * A031873 A075356 A235355

Adjacent sequences: A228431 A228432 A228433 * A228435 A228436 A228437

Keyword

nonn

Author

K. D. Bajpai, Nov 10 2013

Status

approved