OFFSET
1,4
REFERENCES
F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 246.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..85
FORMULA
a(n) = floor( 2^binomial(n,2) / n! ).
MAPLE
A003091:n->floor(2^(n*(n-1)/2)/n!);
MATHEMATICA
Table[Floor[2^(n*(n-1)/2)/n!], {n, 30}] (* G. C. Greubel, Nov 02 2022 *)
PROG
(Magma) [Floor(2^Binomial(n, 2)/Factorial(n)): n in [1..30]]; // G. C. Greubel, Nov 02 2022
(SageMath) [(2^binomial(n, 2)//factorial(n)) for n in range(1, 30)] # G. C. Greubel, Nov 02 2022
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved