OFFSET
0,2
COMMENTS
Let R be a binary relation on [n]. Then x in [n] is a symmetric point of R if there is a y in [n] with x != y and both (x,y),(y,x) in R.
FORMULA
E.g.f.: A(exp(y*x) - 1 - y*x + 2*x) where A(x) is the e.g.f. for A001035.
EXAMPLE
1,
2, 0,
12, 0, 1,
152, 0, 18, 1,
3504, 0, 456, 24, 10,
135392, 0, 17520, 760, 600, 31
MATHEMATICA
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Geoffrey Critzer, Jul 16 2022
STATUS
approved