A321487 Numbers in A121707 (n^3 > 1 divides Sum_{k=1..n-1} k^n) which are not semiprimes.

275, 455, 475, 539, 575, 715, 775, 875, 935, 1075, 1127, 1175, 1235, 1295, 1375, 1421, 1463, 1475, 1495, 1547, 1595, 1615, 1675, 1715, 1775, 1859, 1955, 1975, 2009, 2015, 2035, 2057, 2075, 2093, 2135, 2255, 2261, 2299, 2303, 2375, 2387, 2555, 2575, 2597, 2635, 2639, 2675, 2717, 2783

Offset: 1

Author

M. F. Hasler, Nov 11 2018

Keywords

• nonn

Comments

Most terms of A121707 and its (conjectured) subsequence A267999 are semiprimes. This sequence lists the exceptions.

At first, it looked as if most terms were multiples of 5. The first exceptions are a({4, 11, 16}) = {539, 1127, 1421}. However, after the first 30 terms, almost every other term is not divisible by 5.

The first terms not in A267999 are {2057, 2873, 3689, 4015, 4991, 6137, ...}, cf. A321488.

Links

• M. F. Hasler, Table of n, a(n) for n = 1..2500

Crossrefs

Cf. A121706, A267999, A319386, A306097.