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 A094156 #17 Nov 08 2022 08:06:46 %S A094156 1,4,39,1219,83435,9223092,1453132944,307690667072,84241805734539, %T A094156 28963120073957838,12217399235411398127,6204484017822892034404, %U A094156 3734180195629471796396217,2628347798377200707293720724,2139135966227357959535426526975,1993415431315860419823374898234950 %N A094156 Bisection of A000940. %H A094156 S. W. Golomb and L. R. Welch, <a href="http://www.jstor.org/stable/2308978">On the enumeration of polygons</a>, Amer. Math. Monthly, 67 (1960), 349-353. %o A094156 (Python) %o A094156 from sympy import totient, divisors, factorial %o A094156 def A094156(n): return 1 if n == 1 else (sum(totient(m:=(r:=(n<<1)+1)//d)**2*factorial(d)*m**d for d in divisors((n<<1)+1,generator=True))>>2)//r**2+(1<<n-2)*factorial(n) # _Chai Wah Wu_, Nov 07 2022 %Y A094156 Cf. A000940, A094157. %K A094156 nonn %O A094156 1,2 %A A094156 _N. J. A. Sloane_, May 05 2004