A290881 E.g.f. S(x) satisfies: C(x)^2 - S(x)^2 = 1 and C'(x)^2 + S'(x)^2 = 1, where C(x) is the e.g.f. of A290880.

1, -1, 25, -1705, 227665, -50333425, 16655398825, -7711225809625, 4760499335502625, -3779764853639958625, 3752942823715824285625, -4556465805050372544735625, 6641455313355871353308640625, -11445605320939175012746492140625, 23021828780691053491298409381015625, -53450977127256739279274500814544765625

Offset

1,3

Links

Paul D. Hanna, Table of n, a(n) for n = 1..100

Formula

E.g.f.: S(x) = Series_Reversion( Integral sqrt( (1 + 2*x^2) / (1 + x^2) ) dx ).

E.g.f.: S(x) = sinh( Series_Reversion( Integral sqrt( cosh(2*x) ) dx ) ).

Let C(x) be the e.g.f. of A290880, then:

(1) C'(x) = S(x) / sqrt(C(x)^2 + S(x)^2),

(2) S'(x) = C(x) / sqrt(C(x)^2 + S(x)^2),

such that C(x)^2 - S(x)^2 = 1 and C'(x)^2 + S'(x)^2 = 1.

Example

E.g.f.: S(x) = x - x^3/3! + 25*x^5/5! - 1705*x^7/7! + 227665*x^9/9! - 50333425*x^11/11! + 16655398825*x^13/13! - 7711225809625*x^15/15! + 4760499335502625*x^17/17! - 3779764853639958625*x^19/19! + 3752942823715824285625*x^21/21! +...
such that C(x)^2 - S(x)^2 = 1 where C(x) begins:
C(x) = 1 + x^2/2! - 7*x^4/4! + 265*x^6/6! - 24175*x^8/8! + 4037425*x^10/10! - 1070526775*x^12/12! + 412826556025*x^14/14! - 218150106913375*x^16/16! + 151297155973926625*x^18/18! - 133288452772763494375*x^20/20! +...

Prog

(PARI) {a(n) = my(C=1, S=x); for(i=1, n, C = 1 + intformal( S/sqrt(C^2 + S^2 + O(x^(2*n+2))) ); S = intformal( C/sqrt(C^2 + S^2)) ); (2*n-1)!*polcoeff(S, 2*n-1)}
for(n=1, 20, print1(a(n), ", "))
(PARI) {a(n) = my(C=1); S = serreverse( intformal( sqrt( (1+2*x^2) / (1+x^2 + O(x^(2*n+2))) ) )); (2*n-1)!*polcoeff(S, 2*n-1)}
for(n=1, 20, print1(a(n), ", "))
(PARI) {a(n) = my(S=x); S = sinh( serreverse( intformal( sqrt(cosh(2*x + O(x^(2*n+2)))) ) )); (2*n-1)!*polcoeff(S, 2*n-1)}
for(n=1, 20, print1(a(n), ", "))

Crossrefs

Cf. A290879, A290880, A290882, A290883, A153302.

Sequence in context: A196684 A125826 A263967 * A316911 A212333 A187404

Adjacent sequences: A290878 A290879 A290880 * A290882 A290883 A290884

Keyword

sign

Author

Paul D. Hanna, Aug 13 2017

Status

approved