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 A155210 G.f.: A(x) = exp( Sum_{n>=1} (4^n - 1)^n/3^(n-1) * x^n/n ), a power series in x with integer coefficients. 4
 1, 3, 42, 9378, 39179127, 2766569881269, 3234201150559172040, 62076685218110095082936700, 19446778350632942283719042004313725, 98999235365955012033013202024947235500115415 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS More generally, for m integer, exp( Sum_{n>=1} (m^n - 1)^n/(m-1)^(n-1) * x^n/n ) is a power series in x with integer coefficients. Note that g.f. exp( Sum_{n>=1} (4^n - 1)^n/3^n * x^n/n ) has fractional coefficients as a power series in x. LINKS EXAMPLE G.f.: A(x) = 1 + 3*x + 42*x^2 + 9378*x^3 + 39179127*x^4 +... log(A(x)) = 3*x + 15^2/3*x^2/2 + 63^3/3^2*x^3/3 + 255^4/3^3*x^4/4 +... PROG (PARI) {a(n)=polcoeff(exp(sum(m=1, n+1, (4^m-1)^m/3^(m-1)*x^m/m)+x*O(x^n)), n)} CROSSREFS Cf. A155207, A155208, A155209, variant: A155206. Sequence in context: A213956 A157552 A058808 * A157572 A332973 A137192 Adjacent sequences:  A155207 A155208 A155209 * A155211 A155212 A155213 KEYWORD nonn AUTHOR Paul D. Hanna, Feb 04 2009 STATUS approved

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Last modified August 12 07:45 EDT 2022. Contains 356067 sequences. (Running on oeis4.)