A094156 Bisection of A000940.

1, 4, 39, 1219, 83435, 9223092, 1453132944, 307690667072, 84241805734539, 28963120073957838, 12217399235411398127, 6204484017822892034404, 3734180195629471796396217, 2628347798377200707293720724, 2139135966227357959535426526975, 1993415431315860419823374898234950

Offset: 1

Author

N. J. A. Sloane, May 05 2004

Keywords

• nonn

Links

• S. W. Golomb and L. R. Welch, On the enumeration of polygons, Amer. Math. Monthly, 67 (1960), 349-353.

Crossrefs

Cf. A000940, A094157.

Programs

Python

from sympy import totient, divisors, factorial
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<Chai Wah Wu, Nov 07 2022