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 A259506 #16 Nov 22 2015 15:14:41
%S A259506 0,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,0,0,0,0,0,0,0,1,1,1,1,1,2,2,2,
%T A259506 2,3,3,3,3,4,4,4,5,5,5,5,6,6,6,7,7,7,8,8,8,9,9,9,10,10,10,11,11,11,12,
%U A259506 12,12,13,13,13,14,14,15,15,15,16,16,16,17,17,18
%N A259506 a(n) = floor((LogGamma(n/2+1) - n*log(Pi)/2)/Pi).
%C A259506 Let f(n) = number of (nontrivial) zeros of zeta(z) with 0 < Im(z) < n; then f(n) ~ a(n).
%C A259506 The sequence gives exactly the values of A072080(n) for n = 2, 3, and 5.
%H A259506 <a href="/index/Z#zeta_function">Index entries for zeta function</a>
%F A259506 a(n) = floor((LogGamma(n/2+1) - n*log(Pi)/2)/Pi).
%t A259506 Table[Floor[(LogGamma[n/2 + 1] - n*Log[Pi]/2)/Pi], {n, 0, 74}]
%o A259506 (PARI) a(n)=floor((lngamma(n/2+1)-n*log(Pi)/2)/Pi)
%Y A259506 Cf. A002410, A072080, A082668, A254297.
%K A259506 sign
%O A259506 0,26
%A A259506 _Arkadiusz Wesolowski_, Nov 08 2015