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 A071598 #12 Jul 29 2024 06:18:02
%S A071598 1,7,34,115,298,677,1431,2853,5401,9813,17289,29687,49901,82315,
%T A071598 133617,213801,337742,527231,814218,1244962,1886069,2833392,4223121,
%U A071598 6247850,9179762,13399951,19440903,28043882,40233399,57423953,81557903
%N A071598 a(0) = 1; a(n) = half of the a(n-1)-th even nontotient number.
%e A071598 a(5) = 677 = 1354/2, where 1354 is the a(4) = 298th term in A005277. [Corrected by _Sean A. Irvine_, Jul 28 2024]
%t A071598 a = Table[0, {10^6}]; Do[b = EulerPhi[n]/2; If[b < 10^6 + 1, a[[b]] = 1], {n, 1, 2 10^7}]; b = Select[ Range[10^6], a[[ # ]] == 0 &]; c = 1; Do[ Print[c]; c = b[[c]], {n, 0, 18}]
%Y A071598 Cf. A005277, A072416.
%K A071598 nonn
%O A071598 0,2
%A A071598 _Robert G. Wilson v_, Jun 20 2002
%E A071598 a(19)-a(30) from _Donovan Johnson_, May 30 2010