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A263185
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E.g.f. is the series S(x) such that C(x) + i*S(x) = 1 + i * Integral C(x)/(C(x) + i*S(x)) dx, odd powers only, where i^2 = -1.
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1
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1, -2, 64, -5648, 975616, -278461952, 118706427904, -70671453390848, 56012750847410176, -57020502591712919552, 72506220900036949049344, -112627507642042025532981248, 209858299334586249702944014336, -461985929466656996121846430564352, 1186250077023681407956558109929897984, -3513906471607754874921241344634989314048, 11894054527075875087089375010293820996714496
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OFFSET
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1,2
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LINKS
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Table of n, a(n) for n=1..17.
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FORMULA
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Let C = C(x) and S = S(x) satisfy
(*) C + I*S = 1 + i * Integral C/(C + i*S) dx
then C and S also satisfy
(1) C^2 - S^2 = 1
(2) C*C' - S*S' = 0
(3) C*S' + S*C' = C
(4) S' = C^2/(C^2 + S^2)
(5) C' = C*S/(C^2 + S^2)
(6) C*S = Integral C dx
(7) C + i*S = exp( i * Integral C/(C + I*S)^2 dx ).
...
E.g.f.: Series_Reversion(2*x - arctan(x)). - Paul D. Hanna, Oct 15 2015
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EXAMPLE
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E.g.f.: S(x) = x - 2*x^3/3! + 64*x^5/5! - 5648*x^7/7! + 975616*x^9/9! - 278461952*x^11/11! + 118706427904*x^13/13! - 70671453390848*x^15/15! + 56012750847410176*x^17/17! + ...
RELATED SERIES:
(a) C(x) = 1 + x^2/2! - 11*x^4/4! + 589*x^6/6! - 73079*x^8/8! + 16276921*x^10/10! - 5689569731*x^12/12! + 2870590000069*x^14/14! - 1974092553870959*x^16/16! + ...
(b) C(x)^2 = 1 + 2*x^2/2! - 16*x^4/4! + 848*x^6/6! - 104704*x^8/8! + 23255552*x^10/10! - 8114200576*x^12/12! + 4088708507648*x^14/14! - 2809153285586944*x^16/16! + ...
(c) S(x)^2 = 2*x^2/2! - 16*x^4/4! + 848*x^6/6! - 104704*x^8/8! + 23255552*x^10/10! -+ ...
(d) sqrt(C(x)^2 + S(x)^2) = 1 + 2*x^2/2! - 28*x^4/4! + 1688*x^6/6! - 226672*x^8/8! + 53581472*x^10/10! - 19645025728*x^12/12! + 10314899562368*x^14/14! - 7340759012323072*x^16/16! + ...
(e) log(C(x) + I*S(x)) = I*x + 2*x^2/2! - 7*I*x^3/3! - 40*x^4/4! + 293*I*x^5/5! + 2768*x^6/6! - 30763*I*x^7/7! - 405760*x^8/8! + 6040937*I*x^9/9! + 102313472*x^10/10! -+ ...
(f) arcsinh(S(x)) = x - 3*x^3/3! + 93*x^5/5! - 8127*x^7/7! + 1397337*x^9/9! - 397761243*x^11/11! + 169266767733*x^13/13! - 100648672656087*x^15/15! + ...
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PROG
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(PARI) {a(n) = my(CS=1+x); for(i=1, 2*n, CS = 1 + I*intformal( (CS+conj(CS))/2 / CS +O(x^(2*n+2))) ); (2*n-1)!*polcoeff(imag(CS), 2*n-1)}
for(n=1, 20, print1(a(n), ", "))
(PARI) {a(n) = (2*n-1)! * polcoeff( serreverse(2*x - atan(x +O(x^(2*n)))), 2*n-1)}
for(n=1, 20, print1(a(n), ", "))
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CROSSREFS
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Cf. A263184.
Sequence in context: A300640 A054956 A210930 * A155957 A085535 A060613
Adjacent sequences: A263182 A263183 A263184 * A263186 A263187 A263188
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KEYWORD
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sign
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AUTHOR
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Paul D. Hanna, Oct 11 2015
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STATUS
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approved
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