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 A026119 #21 Feb 22 2023 01:42:57
%S A026119 1,2,4,10,30,94,316,1096,3856,13798,49940,182362,671092,2485534,
%T A026119 9256396,34636834,130150588,490853416,1857283156,7048151672,
%U A026119 26817356776,102280151422,390937468408,1497207322930,5744387279818,22076468764192
%N A026119 Bisection of A000016 (also of A000013).
%H A026119 Seiichi Manyama, <a href="/A026119/b026119.txt">Table of n, a(n) for n = 0..1666</a>
%F A026119 a(n) = (Sum_{d | 2n+1} phi(d)*2^((2n+1)/d)) / (4n+2).
%o A026119 (PARI) a(n) = sumdiv(2*n+1, d, eulerphi(d)*2^((2*n+1)/d)) / (4*n+2); \\ _Michel Marcus_, Sep 11 2013
%o A026119 (Python)
%o A026119 from sympy import totient, divisors
%o A026119 def A026119(n):
%o A026119 m = (n<<1)+1
%o A026119 return sum(totient(d)<<m//d-1 for d in divisors(m,generator=True))//m # _Chai Wah Wu_, Feb 21 2023
%Y A026119 Cf. A000013, A000016, A000116.
%Y A026119 Bisection of A053634 and A053656.
%K A026119 nonn
%O A026119 0,2
%A A026119 _N. J. A. Sloane_, Apr 12 2000