The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A321487 Numbers in A121707 (n^3 > 1 divides Sum_{k=1..n-1} k^n) which are not semiprimes. 3
 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 (list; graph; refs; listen; history; text; internal format)
 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified April 18 08:27 EDT 2024. Contains 371769 sequences. (Running on oeis4.)