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 A154586 #17 Feb 04 2018 03:19:29
%S A154586 1,4,8,25,27,75,209,3507,8466,16179,29285,33987,175904,326764,1161207
%N A154586 Numbers n for which abs((-1)^k*Sum_{k=1..n} ((n-k+1) mod k)) = 0.
%C A154586 Subset of A154585.
%C A154586 a(16) > 10^7. - _Donovan Johnson_, Oct 03 2011
%F A154586 abs{(-1)^k*A004125} = 0
%F A154586 {a(n): A154585(a(n))=0}. - _R. J. Mathar_, Jan 14 2009
%e A154586 n=8 -> abs(-(8 mod 1) + (7 mod 2) - (6 mod 3) + (5 mod 4) - (4 mod 5) + (3 mod 6) - (2 mod 7) + (1 mod 8)) = abs(-0 + 1 - 0 + 1 - 4 + 3 - 2 + 1) = abs(0) = 0.
%p A154586 P:=proc(i) local a,n; for n from 1 to i do a:=abs(add((-1)^k*((n-k+1) mod k),k=1..n)); if a=0 then print(n); fi; od; end: P(100);
%o A154586 (C) #include <stdio.h> int main(int argc, char * argv[]) { for(int n=1;;n++) { unsigned long long a = 0; for(int k=1;k <=n;k += 2) a -= (n-k+1) % k ; for(int k=2;k <=n;k += 2) a += (n-k+1) % k ; if ( a == 0) printf("%d,\n",n) ; } } /* _R. J. Mathar_, Jan 14 2009 */
%Y A154586 Cf. A004125, A154585.
%K A154586 more,nonn
%O A154586 1,2
%A A154586 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jan 12 2009
%E A154586 8466 inserted, and sequence extended up to a(13), by _R. J. Mathar_, Jan 14 2009
%E A154586 a(14)-a(15) from _Donovan Johnson_, Oct 03 2011