OFFSET
1,4
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..40 (terms 1..22 from R. J. Mathar, terms 21..22 corrected by Andrew Howroyd)
P. Hanlon and R. W. Robinson, Counting bridgeless graphs, J. Combin. Theory, B 33 (1982), 276-305.
PROG
cycleIndexSeries(n)={my(g=graphsSeries(n), gcr=sPoint(g)/g); sSolve( gcr, x*sv(1)*sExp(gcr) )}
NumUnlabeledObjsSeq(cycleIndexSeries(15)) \\ Andrew Howroyd, Dec 27 2020
CROSSREFS
KEYWORD
nonn,nice
AUTHOR
EXTENSIONS
Reference gives first 22 terms (terms a(21) and a(22) contain typos).
More terms from R. J. Mathar, Jun 06 2007
STATUS
approved