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 A290347 #13 Apr 04 2025 22:46:31
%S A290347 0,1,6,26,100,1096,3920,13936,16544,296256,1068672,11652352,42658304,
%T A290347 1100471296,4079876096,15205967872,56939270144,642281037824,
%U A290347 2423854317568,9177027411968,34846713511936,1459319692460032,5568939824513024,21297365878571008
%N A290347 Numerators of the Harary index for the n-halved cube graph.
%C A290347 For p > 3, if p is prime, then p^2 divides a(p). Conjecture: for n > 3, if n^2 divides a(n), then n is prime. Primes p such that p^3 diviedes a(p) are probably A088164. - _Thomas Ordowski_, Mar 30 2025
%H A290347 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HararyIndex.html">Harary Index</a>
%H A290347 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HalvedCubeGraph.html">Halved Cube Graph</a>
%F A290347 a(n) = -2^(n-1)*HarmonicNumber(n)-2^(2*n-1)*Re(LerchPhi(2,1,n+1)).
%F A290347 For n > 1, A000265(a(n)) = A330718(n). - _Thomas Ordowski_, Mar 30 2025
%e A290347 First few terms are 0, 1, 6, 26, 100, 1096/3, 3920/3, 13936/3, 16544, 296256/5, ....
%t A290347 Table[-2^(n - 1) HarmonicNumber[n] - 2^(2 n - 1) Re[LerchPhi[2, 1, n + 1]], {n, 20}] // Numerator
%Y A290347 Cf. A000265, A088164, A290348 (denominators), A330718.
%K A290347 nonn,frac
%O A290347 1,3
%A A290347 _Eric W. Weisstein_, Jul 28 2017