OFFSET
1,1
REFERENCES
W. Oberschelp, "Strukturzahlen in endlichen Relationssystemen", in Contributions to Mathematical Logic (Proceedings 1966 Hanover Colloquium), pp. 199-213, North-Holland Publ., Amsterdam, 1968.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..7
P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5.
W. Oberschelp, Strukturzahlen in endlichen Relationssystemen, in Contributions to Mathematical Logic (Proceedings 1966 Hanover Colloquium), pp. 199-213, North-Holland Publ., Amsterdam, 1968. [Annotated scanned copy]
PROG
(Python)
from itertools import product
from math import factorial, prod, lcm
from fractions import Fraction
from sympy.utilities.iterables import partitions
def A001377(n): return int(sum(Fraction(1<<sum(prod(r)//lcm(*r)*prod(p[d] for d in r) for r in product(p.keys(), repeat=4)), prod(q**p[q]*factorial(p[q]) for q in p)) for p in partitions(n))) # Chai Wah Wu, Jul 02 2024
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
EXTENSIONS
More terms from Vladeta Jovovic
STATUS
approved