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 A072077 #13 Jun 20 2024 02:38:44
%S A072077 0,0,0,1,2,6,17,41,94,215,470,1004,2126,4449,9278,19177,39388,80698,
%T A072077 164808,335809,683117,1387415,2813664,5700228,11536241,23324624,
%U A072077 47122764,95134678,191937316,387024829,780018815,1571331010,3164113363
%N A072077 Number of even nontotients not exceeding 2^n.
%C A072077 Number of terms in A005277 <= 2^n.
%e A072077 For n = 6: a(6) = 6 because the even nontotients not exceeding 64 are {14,26,34,38,50,62}.
%t A072077 a = Table[0, {2^26}]; Do[ b = EulerPhi[n]; If[ EvenQ[b] && b < 2^27, a[[b/2]]++ ], {n, 3, 10^9}]; c = 0; k = 1; Do[ While[k <= 2^n, If[ a[[k]] == 0, c++ ]; k++ ]; Print[c], {n, 1, 17}]
%o A072077 (PARI) lista(kmax) = {my(c = 0, p = 2); forstep(k = 2, kmax, 2, if(!istotient(k), c++); if(k == p, print1(c, ", "); p *= 2));} \\ _Amiram Eldar_, Jun 20 2024
%Y A072077 Cf. A000079, A005277.
%K A072077 nonn,hard,more
%O A072077 1,5
%A A072077 _Labos Elemer_, Jun 13 2002
%E A072077 Edited and extended by _Robert G. Wilson v_, Jul 15 2002
%E A072077 a(27)-a(32) from _Donovan Johnson_, Jun 03 2013
%E A072077 a(33) from _Amiram Eldar_, Jun 20 2024