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 A251684 G.f.: exp( Sum_{n>=1} A047863(n)*x^n/n ), where A047863(n) = Sum_{k=0..n} binomial(n, k) * (2^k)^(n-k). 0
 1, 2, 5, 16, 69, 426, 3947, 55612, 1177747, 36816650, 1676270109, 110202314208, 10408422663015, 1407329003121294, 271801891072128621, 74846096423770137324, 29351301902680241116593, 16374214768286861089202358, 12985582377076992552497257703, 14629438237685095017820000611400 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Logarithmic derivative yields A047863, the number of labeled graphs with 2-colored nodes where black nodes are only connected to white nodes and vice versa. LINKS EXAMPLE G.f.: A(x) = 1 + 2*x + 5*x^2 + 16*x^3 + 69*x^4 + 426*x^5 + 3947*x^6 +... where the logarithmic derivative yields A047863: A'(x)/A(x) = 2 + 6*x + 26*x^2 + 162*x^3 + 1442*x^4 + 18306*x^5 + 330626*x^6 + 8488962*x^7 + 309465602*x^8 +...+ A047863(n+1)*x^n +... PROG (PARI) {A047863(n) = sum(k=0, n, binomial(n, k) * (2^k)^(n-k) )} {a(n)=local(A); A=exp(sum(k=1, n+1, A047863(k)*x^k/k) +x*O(x^n)); polcoeff(A, n)} for(n=0, 20, print1(a(n), ", ")) CROSSREFS Cf. A047863. Sequence in context: A296675 A059295 A259408 * A129092 A110710 A245881 Adjacent sequences:  A251681 A251682 A251683 * A251685 A251686 A251687 KEYWORD nonn AUTHOR Paul D. Hanna, Feb 14 2015 STATUS approved

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Last modified September 21 16:31 EDT 2021. Contains 347598 sequences. (Running on oeis4.)