A321487 - OEIS

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

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OFFSET

1,1

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.

Sequence in context: A062377 A157489 A144715 * A250736 A063368 A028531

Adjacent sequences: A321484 A321485 A321486 * A321488 A321489 A321490

KEYWORD

nonn

AUTHOR

M. F. Hasler, Nov 11 2018

STATUS

approved