A094157 Bisection of A000940.

2, 12, 202, 9468, 836017, 111255228, 20433309147, 4940118795869, 1520564059349452, 580578894859915650, 269291841184184374868, 149146250420586942401004, 97222048664558428304285193, 73681349947834075264704425280, 64240926985765124116695616020874, 63847923667734462963941294951243328

Offset

2,1

Links

Table of n, a(n) for n=2..17.

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

Prog

(Python)
from sympy import factorial, divisors, totient
def A094157(n): return 2 if n == 2 else ((sum(totient(m:=(r:=n<<1)//d)**2*factorial(d)*m**d for d in divisors(n<<1, generator=True))+(1<<n-2)*r*(r+6)*factorial(n))>>2)//r**2 # Chai Wah Wu, Nov 07 2022

Crossrefs

Cf. A000940, A094156.

Sequence in context: A245358 A317350 A209832 * A306715 A012598 A156489

Adjacent sequences: A094154 A094155 A094156 * A094158 A094159 A094160

Keyword

nonn

Author

N. J. A. Sloane, May 05 2004

Status

approved