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A118934 E.g.f.: exp(x + x^4/4). 4
1, 1, 1, 1, 7, 31, 91, 211, 1681, 12097, 57961, 209881, 1874071, 17842111, 117303187, 575683291, 5691897121, 65641390081, 544238393041, 3362783785777, 36455473647271, 485442581801311, 4828464958268491, 35900587138847971 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

Equals row sums of triangle A118933.

These are the telephone numbers T^(4)_n of [Artioli et al., p. 7]. - Eric M. Schmidt, Oct 12 2017

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Marcello Artioli, Giuseppe Dattoli, Silvia Licciardi, and Simonetta Pagnutti, Motzkin Numbers: an Operational Point of View, arXiv:1703.07262 [math.CO], 2017.

Vaclav Kotesovec, Graph - asymptotic (20000 terms)

FORMULA

a(n) = a(n-1) + (n-1)*(n-2)*(n-3)*a(n-4) for n>=4, with a(0)=a(1)=a(2)=a(3)=1.

a(n) ~ 1/2 * n^(3*n/4) * exp(n^(1/4)-3*n/4). - Vaclav Kotesovec, Feb 25 2014

a(n) = Sum_{k=0..floor(n/4)} n!/(4^k*k!*(n-4*k)!). - G. C. Greubel, Mar 07 2021

MATHEMATICA

With[{nn=30}, CoefficientList[Series[Exp[x+x^4/4], {x, 0, nn}], x]Range[0, nn]!] (* Harvey P. Dale, Jan 26 2013 *)

Table[Sum[n!/(4^k*k!*(n-4*k)!), {k, 0, n/4}], {n, 0, 30}]

PROG

(PARI) a(n)=if(n<0, 0, if(n==0, 1, a(n-1) + (n-1)*(n-2)*(n-3)*a(n-4)))

(Sage) f=factorial; [sum(f(n)/(4^j*f(j)*f(n-4*j)) for j in (0..n/4)) for n in (0..30)] # G. C. Greubel, Mar 07 2021

(Magma) F:=Factorial; [(&+[F(n)/(4^j*F(j)*F(n-4*j)): j in [0..Floor(n/4)]]): n in [0..30]]; // G. C. Greubel, Mar 07 2021

CROSSREFS

Sequences with e.g.f. exp(x + x^m/m): A000079 (m=1), A000085 (m=2), A001470 (m=3), this sequence (m=4), A052501 (m=5), A293588 (m=6), A053497 (m=7).

Cf. A118933.

Sequence in context: A202254 A305290 A262012 * A118935 A226838 A205801

Adjacent sequences: A118931 A118932 A118933 * A118935 A118936 A118937

KEYWORD

nonn

AUTHOR

Paul D. Hanna, May 06 2006

STATUS

approved

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Last modified November 28 21:48 EST 2022. Contains 358421 sequences. (Running on oeis4.)