A227887 O.g.f.: 1/(1 - x/(1 - 2^4*x/(1 - 3^4*x/(1 - 4^4*x/(1 - 5^4*x/(1 - 6^4*x/(1 -...))))))), a continued fraction.

1, 1, 17, 1585, 485729, 372281761, 601378506737, 1820943071778385, 9489456505643743169, 79759396929125826861121, 1027412704023984825792488657, 19464301715272748317827942755185, 524230105465412991467916306841439009, 19509134827116013764271741468197795034081

Offset

0,3

Comments

Compare to the continued fraction for the Euler numbers (A000364):

1/(1-x/(1-2^2*x/(1-3^2*x/(1-4^2*x/(1-5^2*x/(1-6^2*x/(1-...))))))).

From Vaclav Kotesovec, Sep 24 2020: (Start)

In general, if s>0 and g.f. = 1/(1 - x/(1 - 2^s*x/(1 - 3^s*x/(1 - 4^s*x/(1 - 5^s*x/(1 - 6^s*x/(1 -...))))))), a continued fraction, then

a(n,s) ~ c(s) * d(s)^n * (n!)^s / sqrt(n), where

d(s) = (2*s*Gamma(2/s) / Gamma(1/s)^2)^s

c(s) = sqrt(s*d(s)/(2*Pi)). (End)

Links

Table of n, a(n) for n=0..13.

Formula

a(n) ~ c * d^n * (n!)^4 / sqrt(n), where d = 4096 * Pi^2 / Gamma(1/4)^8 = 1.353976395034780345656335026823167975194... and c = sqrt(2*d/Pi) = 64 * sqrt(2*Pi) / Gamma(1/4)^4 = 0.9284223954634658948993105287957575... - Vaclav Kotesovec, Aug 25 2017, updated Sep 23 2020

Example

G.f.: A(x) = 1 + x + 17*x^2 + 1585*x^3 + 485729*x^4 + 372281761*x^5 +...

Maple

T := proc(n, k) option remember; if k = 0 then 1 else if k = n then T(n, k-1)
else (k - n - 1)^4 * T(n, k - 1) + T(n - 1, k) fi fi end:
a := n -> T(n, n): seq(a(n), n = 0..13);  # Peter Luschny, Oct 02 2023

Mathematica

nmax = 20; CoefficientList[Series[1/Fold[(1 - #2/#1) &, 1, Reverse[Range[nmax + 1]^4*x]], {x, 0, nmax}], x] (* Vaclav Kotesovec, Aug 25 2017 *)

Prog

(PARI) {a(n)=local(CF=1+x*O(x^n)); for(k=1, n, CF=1/(1-(n-k+1)^4*x*CF)); polcoeff(CF, n)}
for(n=0, 20, print1(a(n), ", "))

Crossrefs

Cf. A000364, A216966, A337807, A337808, A337809.

Sequence in context: A104808 A061686 A133590 * A144571 A242228 A373856

Adjacent sequences: A227884 A227885 A227886 * A227888 A227889 A227890

Keyword

nonn

Author

Paul D. Hanna, Oct 26 2013

Status

approved