%I #19 Jan 17 2020 14:05:53

%S 275,455,475,539,575,715,775,875,935,1075,1127,1175,1235,1295,1375,

%T 1421,1463,1475,1495,1547,1595,1615,1675,1715,1775,1859,1955,1975,

%U 2009,2015,2035,2057,2075,2093,2135,2255,2261,2299,2303,2375,2387,2555,2575,2597,2635,2639,2675,2717,2783

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

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

%C 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.

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

%H M. F. Hasler, <a href="/A321487/b321487.txt">Table of n, a(n) for n = 1..2500</a>

%Y Cf. A121706, A267999, A319386, A306097.

%K nonn

%O 1,1

%A _M. F. Hasler_, Nov 11 2018