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 A283847 #25 Mar 09 2025 12:27:39
%S A283847 2,8,36,140,522,1920,7030,25704,94302,347488,1286460,4785300,17879352,
%T A283847 67076096,252579600,954306220,3616552422,13743371072,52356648380,
%U A283847 199909107900,764873459802,2932022620160,11258982291252,43303809016440,166799919094902,643371241120928
%N A283847 Number of n-gonal inositol homologs with 2 kinds of achiral proligands.
%H A283847 Robert Israel, <a href="/A283847/b283847.txt">Table of n, a(n) for n = 3..1665</a>
%H A283847 Shinsaku Fujita, <a href="https://doi.org/10.1246/bcsj.20160369">alpha-beta Itemized Enumeration of Inositol Derivatives and m-Gonal Homologs by Extending Fujita's Proligand Method</a>, Bull. Chem. Soc. Jpn. 2017, 90, 343-366; doi:10.1246/bcsj.20160369. See Table 8.
%F A283847 a(n) = (4*n)^(-1)*(Sum_{d|n, d odd} phi(d)*4^(n/d)) - 2^(n-1). - _Robert Israel_, Aug 23 2018 after Fujita (2017), Eq. (100) (set n=2, m=n)
%p A283847 f:= proc(n) uses numtheory;
%p A283847 if n::even then (4*n)^(-1)*add(phi(d)*4^(n/d), d = select(type,divisors(n),odd)) - 2^(n-1)
%p A283847 else (4*n)^(-1)*add(phi(d)*4^(n/d), d = divisors(n)) - 2^(n-1)
%p A283847 fi
%p A283847 end proc:
%p A283847 map(f, [$3..50]); # _Robert Israel_, Aug 23 2018
%t A283847 a[n_] := If[EvenQ[n], (4n)^(-1) Sum[EulerPhi[d] 4^(n/d), {d, Select[ Divisors[n], OddQ]}] - 2^(n-1), (4n)^(-1) Sum[EulerPhi[d] 4^(n/d), {d, Divisors[n]}] - 2^(n-1)];
%t A283847 Table[a[n], {n, 3, 50}] (* _Jean-François Alcover_, Mar 23 2019, after _Robert Israel_ *)
%Y A283847 The 8 sequences in Table 8 of Fujita (2017) are A053656, A000011, A256216, A256217, A123045, A283846, A283847, A283848.
%K A283847 nonn
%O A283847 3,1
%A A283847 _N. J. A. Sloane_, Apr 01 2017