A337343 Numbers k such that A064989(sigma(k)) >= k.

1, 2, 4, 9, 16, 18, 25, 36, 50, 64, 100, 144, 225, 256, 289, 400, 450, 576, 578, 729, 784, 900, 1024, 1156, 1296, 1458, 1600, 1681, 1764, 1800, 1936, 2304, 2401, 2601, 2704, 2916, 3136, 3362, 3481, 3600, 4096, 4356, 4624, 4802, 4900, 5041, 5184, 5202, 5328, 5776, 5832, 6084, 6400, 6561, 6724, 6962, 7056, 7225, 7744, 7921, 8192

Offset: 1

Author

Antti Karttunen, Aug 26 2020

Keywords

• nonn

Comments

Not all terms are squares or twice squares: the first terms not in A028982 are: 5328, 8784, 22608, 27792, 35136, 39888, 45072, 57168, 58320, 60624, ...

Crossrefs

Cf. A000203, A028982, A064989, A337344 (odd terms).

Programs

PARI

A064989(n) = {my(f); f = factor(n); if((n>1 && f[1,1]==2), f[1,2] = 0); for (i=1, #f~, f[i,1] = precprime(f[i,1]-1)); factorback(f)};
isA337343(n) = (A064989(sigma(n))>=n);