A280286 a(n) is the least k such that sopfr(k) - sopf(k) = n.

4, 9, 8, 25, 16, 49, 32, 81, 64, 121, 128, 169, 256, 625, 512, 289, 1024, 361, 2048, 1444, 1331, 529, 5324, 2116, 2197, 4232, 8788, 841, 17576, 961, 7569, 3844, 4913, 7688, 19652, 1369, 6859, 5476, 12321, 1681, 34225, 1849, 15129, 7396, 12167, 2209, 46225, 8836, 19881

Offset

2,1

Links

Michel Marcus, Table of n, a(n) for n = 2..500

Formula

For p prime, a(p) = p^2 (see A001248).

Prog

(PARI) sopfr(n) = my(f=factor(n)); sum(j=1, #f~, f[j, 1]*f[j, 2]);
sopf(n) = my(f=factor(n)); sum(j=1, #f~, f[j, 1]);
a(n) = {my(k = 2); while (sopfr(k) - sopf(k) != n, k++); k; }

Crossrefs

Cf. A001414 (sopfr), A008472 (sopf), A001248, A280163.

Sequence in context: A118585 A067666 A355012 * A268597 A373319 A253560

Adjacent sequences: A280283 A280284 A280285 * A280287 A280288 A280289

Keyword

nonn

Author

Michel Marcus, Dec 31 2016

Status

approved