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A231866 E.g.f. A(x) satisfies: A'(x) = A(x*A'(x)^2) with A(0)=1. 7
1, 1, 1, 5, 53, 909, 22149, 711297, 28687833, 1405408841, 81620841401, 5516637014061, 427699967681709, 37595972586389109, 3711295383595024221, 408142117923542673737, 49663409518409586541937, 6647274714312311181770577, 973638869018128380202018353 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..18.

FORMULA

E.g.f. satisfies: A(x) = A'(x/A(x)^2).

E.g.f. satisfies: A(x) = sqrt( x / Series_Reversion( x*A'(x)^2 ) ).

a(n) = [x^(n-1)/(n-1)!] A(x)^(2*n-1)/(2*n-1) for n>=1.

a(n) == 1 (mod 4) for n>=0.

EXAMPLE

E.g.f.: A(x) = 1 + x + x^2/2! + 5*x^3/3! + 53*x^4/4! + 909*x^5/5! + 22149*x^6/6! +...

such that

A(x*A'(x)^2) = A'(x) = 1 + x + 5*x^2/2! + 53*x^3/3! + 909*x^4/4! + 22149*x^5/5! +...

The square of the e.g.f. begins:

A(x)^2 = 1 + 2*x + 4*x^2/2! + 16*x^3/3! + 152*x^4/4! + 2448*x^5/5! +...

To illustrate a(n) = [x^(n-1)/(n-1)!] A(x)^(2*n-1)/(2*n-1), create a table of coefficients of x^k/k!, k>=0, in A(x)^(2*n-1), n>=1, like so:

A^1 : [1,  1,   1,    5,    53,    909,    22149,    711297, ...];

A^3 : [1,  3,   9,   39,   333,   5007,   112101,   3395907, ...];

A^5 : [1,  5,  25,  145,  1205,  16065,   326525,   9235165, ...];

A^7 : [1,  7,  49,  371,  3437,  44163,   825741,  21682143, ...];

A^9 : [1,  9,  81,  765,  8181, 108981,  1952469,  47966553, ...];

A^11: [1, 11, 121, 1375, 16973, 243639,  4370069, 102669787, ...];

A^13: [1, 13, 169, 2249, 31733, 498537,  9246861, 213557877, ...];

A^15: [1, 15, 225, 3435, 54765, 945195, 18486525, 430317495, ...]; ...

then the diagonal in the above table generates this sequence shift left:

[1/1, 3/3, 25/5, 371/7, 8181/9, 243639/11, 9246861/13, 430317495/15, ...].

PROG

(PARI) {a(n)=local(A=1+x); for(i=1, n, A=1+intformal(subst(A, x, x*A'^2 +x*O(x^n)))); n!*polcoeff(A, n)}

for(n=0, 25, print1(a(n), ", "))

(PARI) {a(n)=local(A=1+x); for(i=1, n, A=1+intformal(sqrt(1/x*serreverse(x/A^2 +x*O(x^n))))); n!*polcoeff(A, n)}

for(n=0, 25, print1(a(n), ", "))

CROSSREFS

Cf. A231619, A231899, A232694, A232695, A232696.

Sequence in context: A090360 A123130 A094089 * A196659 A128943 A180351

Adjacent sequences:  A231863 A231864 A231865 * A231867 A231868 A231869

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Nov 14 2013

STATUS

approved

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Last modified June 24 21:16 EDT 2019. Contains 324337 sequences. (Running on oeis4.)