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A113134 a(0) = a(1) = 1, a(2) = x, a(3) = 2x^2, a(n) = x*(n-1)*a(n-1) + Sum_{j=2..n-2} (j-1)*a(j)*a(n-j), n>=4 and for x = 7. 7
1, 1, 7, 98, 2107, 61054, 2215094, 96203268, 4856212179, 279081882086, 17981777803682, 1283631249683804, 100557420457355358, 8577121056958121836, 791318123914138366924, 78521346319092948749576 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..15.

FORMULA

a(n+1) = Sum{k, 0<=k<=n} 7^k*A113129(n, k).

G.f.: A(x) = x/series_reversion(x*G(x)) where G(x) = g.f. of 7-fold factorials.

G.f. satisfies: A(x*G(x)) = G(x) = g.f. of 7-fold factorials.

EXAMPLE

a(2) = 7.

a(3) = 2*7^2 = 98.

a(4) = 7*3*98 + 1*7*7 = 2107.

a(5) = 7*4*2107 + 1*7*98 + 2*98*7 = 61054.

a(6) = 7*5*61054 + 1*7*2107 + 2*98*98 + 3*2107*7 = 2215094.

G.f.: A(x) = 1 + x + 7*x^2 + 98*x^3 + 2107*x^4 + 61054*x^5

+...

= x/series_reversion(x + x^2 + 8*x^3 + 120*x^4 + 2640*x^5

+...).

MATHEMATICA

x=7; a[0]=a[1]=1; a[2]=x; a[3]=2x^2; a[n_]:=a[n]=x*(n-1)*a[n-1]+Sum[(j-1)*a[j ]*a[n-j], {j, 2, n-2}]; Table[a[n], {n, 0, 16}](Robert G. Wilson v)

PROG

(PARI) a(n)=Vec(x/serreverse(x*Ser(vector(n+1, k, if(k==1, 1, prod(j=0, k-2, 7*j+1))))))[n+1]

(PARI) a(n, x=7)=if(n<0, 0, if(n==0 || n==1, 1, if(n==2, x, if(n==3, 2*x^2,

x*(n-1)*a(n-1)+sum(j=2, n-2, (j-1)*a(j)*a(n-j))))))

CROSSREFS

Cf. A045754, A075834(x=1), A111088(x=2), A113130(x=3), A113131(x=4), A113132(x=5), A113133(x=6), A113135(x=8).

Sequence in context: A156266 A234873 A051188 * A334722 A092818 A238472

Adjacent sequences:  A113131 A113132 A113133 * A113135 A113136 A113137

KEYWORD

nonn

AUTHOR

Philippe Deléham and Paul D. Hanna, Oct 28 2005

STATUS

approved

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Last modified June 6 17:20 EDT 2020. Contains 334829 sequences. (Running on oeis4.)