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 A357804 a(n) = coefficient of x^(4*n+1)/(4*n+1)! in power series S(x) = Series_Reversion( Integral 1/(1 + x^4)^(3/2) dx ). 3

%I #15 Dec 03 2022 12:03:55

%S 1,36,87696,1483707456,91329084354816,14862901723860427776,

%T 5279211177231308343054336,3600188413031639396548043882496,

%U 4300014195136238449156877005063520256,8394333803654997846112872487491938363375616,25378508500092778024069322428694679252236239896576

%N a(n) = coefficient of x^(4*n+1)/(4*n+1)! in power series S(x) = Series_Reversion( Integral 1/(1 + x^4)^(3/2) dx ).

%C Equals row sums of triangle A357800.

%H Paul D. Hanna, <a href="/A357804/b357804.txt">Table of n, a(n) for n = 0..200</a>

%F Generating function S(x) = Sum_{n>=0} a(n)*x^(4*n+1)/(4*n+1)! and related function C(x) satisfies the following formulas.

%F For brevity, some formulas here will use S = S(x) and C = C(x), where C(x) = (1 + S(x)^4)^(1/4) is the e.g.f. of A357805.

%F (1) C(x)^4 - S(x)^4 = 1.

%F Integral formulas.

%F (2.a) S(x) = Integral C(x)^6 dx.

%F (2.b) C(x) = 1 + Integral S(x)^3 * C(x)^3 dx.

%F (2.c) S(x)^4 = Integral 4 * S(x)^3 * C(x)^6 dx.

%F (2.d) C(x)^4 = 1 + Integral 4 * S(x)^3 * C(x)^6 dx.

%F Derivatives.

%F (3.a) d/dx S(x) = C(x)^6.

%F (3.b) d/dx C(x) = S(x)^3 * C(x)^3.

%F Exponential formulas.

%F (4.a) C + S = exp( Integral (C^2 - C*S + S^2) * C^3 dx ).

%F (4.b) C - S = exp( -Integral (C^2 + C*S + S^2) * C^3 dx ).

%F (5.a) C^2 + S^2 = exp( 2 * Integral S*C^4 dx ).

%F (5.b) C^2 - S^2 = exp( -2 * Integral S*C^4 dx ).

%F Hyperbolic functions.

%F (6.a) C = sqrt(C^2 - S^2) * cosh( Integral (C^2 + S^2) * C^3 dx ).

%F (6.b) S = sqrt(C^2 - S^2) * sinh( Integral (C^2 + S^2) * C^3 dx ).

%F (7.a) C^2 = cosh( 2 * Integral S*C^4 dx ).

%F (7.b) S^2 = sinh( 2 * Integral S*C^4 dx ).

%F Explicit formulas.

%F (8.a) S(x) = Series_Reversion( Integral 1/(1 + x^4)^(3/2) dx ).

%F (8.b) C( Integral 1/(1 + x^4)^(3/2) dx ) = (1 + x^4)^(1/4).

%e E.g.f.: S(x) = x + 36*x^5/5! + 87696*x^9/9! + 1483707456*x^13/13! + 91329084354816*x^17/17! + 14862901723860427776*x^21/21! + 5279211177231308343054336*x^25/25! + ...

%e such that

%e S( Integral 1/(1 + x^4)^(3/2) dx ) = x

%e also

%e C(x)^4 - S(x)^4 = 1,

%e where

%e C(x) = 1 + 6*x^4/4! + 8316*x^8/8! + 98843976*x^12/12! + 4698140798736*x^16/16! + 623259279912288096*x^20/20! + 186936162949832833285056*x^24/24! + ... + A357805(n)*x^(4*n)/(4*n)! + ...

%o (PARI) /* Using Series Reversion (faster) */

%o {a(n) = my(S = serreverse( intformal( 1/(1 + x^4 +O(x^(4*n+4)))^(3/2) )) );

%o (4*n+1)!*polcoeff( S, 4*n+1)}

%o for(n=0, 10, print1( a(n), ", "))

%o (PARI) {a(n) = my(S=x, C=1); for(i=0, n,

%o S = intformal( C^6 +O(x^(4*n+4)));

%o C = 1 + intformal( S^3*C^3 ) );

%o (4*n)!*polcoeff( C, 4*n)}

%o for(n=0, 10, print1( a(n), ", "))

%Y Cf. A357805 (C(x)), A357800, A153301.

%K nonn

%O 0,2

%A _Paul D. Hanna_, Oct 14 2022

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Last modified September 12 15:28 EDT 2024. Contains 375853 sequences. (Running on oeis4.)