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 A173313 Partial sums of A000273. 0
 1, 2, 5, 21, 239, 9847, 1550791, 883584231, 1794242777079, 13029751067176631, 341273461704039756983, 32523250658517590150954423, 11366777954076059092024044958647, 14669097059490883945096188099361179575, 70315671284332059012269451652168003452397495 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Partial sums of number of directed graphs (or digraphs) with n nodes. The subsequence of primes in this partial sum begins 2, 5, 239, then no more through a(20). a(n) is the number of isolated points over all directed graphs with (n + 1) nodes. - Geoffrey Critzer, Oct 08 2012 LINKS FORMULA a(n) = Sum_{i=0..n} A000273(i). O.g.f.: A(x)/(1-x) where A(x) is the o.g.f. for A000273. - Geoffrey Critzer, Oct 08 2012 EXAMPLE a(12) = 1 + 1 + 3 + 16 + 218 + 9608 + 1540944 + 882033440 + 1793359192848 + 13027956824399552 + 341260431952972580352 + 32522909385055886111197440 + 11366745430825400574433894004224. MAPLE b:= proc(n, i, l) `if`(n=0 or i=1, 1/n!*2^((p-> add(p[j]-1+add(       igcd(p[k], p[j]), k=1..j-1)*2, j=1..nops(p)))([l[], 1\$n])),       add(b(n-i*j, i-1, [l[], i\$j])/j!/i^j, j=0..n/i))     end: a:= proc(n) option remember; b(n\$2, [])+`if`(n=0, 0, a(n-1)) end: seq(a(n), n=0..16);  # Alois P. Heinz, Sep 04 2019 MATHEMATICA nn=20; d=Sum[NumberOfDirectedGraphs[n]x^n, {n, 0, nn}]; CoefficientList[Series[d/(1-x), {x, 0, nn}], x] CROSSREFS Cf. A000273. Sequence in context: A162437 A216756 A007570 * A210575 A174143 A298762 Adjacent sequences:  A173310 A173311 A173312 * A173314 A173315 A173316 KEYWORD nonn AUTHOR Jonathan Vos Post, Feb 16 2010 STATUS approved

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Last modified January 22 15:58 EST 2022. Contains 350481 sequences. (Running on oeis4.)