This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138586 #7 Sep 26 2024 23:35:05
%S A138586 1,129,280065,4586751489,358322666751489,100306488365546751489,
%T A138586 82606511560391889386751489,173238283180457843219993066751489,
%U A138586 828593116199250458889895450218986751489
%N A138586 a(1) = 1; a(n) = a(n-1) + (n!)^7.
%C A138586 After a(1) = 1 these are all divisible by 3. a(n)/3 is prime (i.e. a(n) is semiprime) for n = 2, 4 (i.e. (1!)^7 + (2!)^7 + (3!)^7 + (4!)^7 = 4586751489 = 3 * 1528917163) and then when next?
%F A138586 a(n) = Sum_{k=1..n} (k!)^7 = Sum_{k=1..n} A001015(A000142(n)).
%Y A138586 Cf. A000142, A001015, A104344, A100288.
%K A138586 easy,nonn
%O A138586 1,2
%A A138586 _Jonathan Vos Post_, May 18 2008