OFFSET
0,6
FORMULA
E.g.f. C(x), where related functions S = S(x), C = C(x), and D = D(x) possess the following properties.
(1.a) C^2 - S^2 = 1.
(1.b) D^3 - S^3 = 1.
Integrals.
(2.a) S = Integral C*D^2 dx.
(2.b) C = 1 + Integral S*D^2 dx.
(2.c) D = 1 + Integral C*S^2 dx.
(2.d) C + S = 1 + Integral (C + S) * D^2 dx.
(2.e) D - S = 1 - Integral (D^2 - S^2) * C dx.
Exponential.
(3.a) C + S = exp( Integral D^2 dx ).
(3.b) D - S = exp( Integral -(D + S) * C dx.
(3.c) C = cosh( Integral D^2 dx ).
(3.d) S = sinh( Integral D^2 dx ).
Derivatives.
(4.a) S' = C*D^2.
(4.b) C' = S*D^2.
(4.c) D' = C*S^2.
(4.d) (C' + S')/(C + S) = D^2.
(4.e) (D' - S')/(D - S) = -(D + S) * C.
EXAMPLE
E.g.f.: C(x) = 1 + x^2/2! + x^4/4! + 20*x^5/5! + x^6/6! + 420*x^7/7! + 1841*x^8/8! + 7140*x^9/9! + 190001*x^10/10! + 555940*x^11/11! + 12774881*x^12/12! + 141201060*x^13/13! + 946212001*x^14/14! + 25228809060*x^15/15! + 202847031121*x^16/16! + 3740829095780*x^17/17! + 66881800434001*x^18/18! +...
such that
(1) C(x)^2 - S(x)^2 = 1,
(2) D(x)^3 - S(x)^3 = 1,
where functions S(x) and D(x) are illustrated below.
RELATED SERIES.
S(x) = x + x^3/3! + 4*x^4/4! + x^5/5! + 100*x^6/6! + 161*x^7/7! + 1764*x^8/8! + 22001*x^9/9! + 49700*x^10/10! + 1649921*x^11/11! + 10057124*x^12/12! + 105372001*x^13/13! + 2044251300*x^14/14! + 12879413281*x^15/15! + 315936586084*x^16/16! + 3892292034001*x^17/17! + 49987743460900*x^18/18! +...
D(x) = 1 + 2*x^3/3! + 20*x^5/5! + 40*x^6/6! + 182*x^7/7! + 3360*x^8/8! + 5320*x^9/9! + 165480*x^10/10! + 1193962*x^11/11! + 7681520*x^12/12! + 182657020*x^13/13! + 1028347320*x^14/14! + 21430373342*x^15/15! + 296385660480*x^16/16! + 2926954283120*x^17/17! + 74104327031560*x^18/18! +...
S(x)^2 = 2*x^2/2! + 8*x^4/4! + 40*x^5/5! + 32*x^6/6! + 1680*x^7/7! + 3808*x^8/8! + 49560*x^9/9! + 646912*x^10/10! + 2192960*x^11/11! + 65759008*x^12/12! + 475555080*x^13/13! + 5786067392*x^14/14! + 114473289840*x^15/15! + 891694992608*x^16/16! + 21934824868600*x^17/17! + 298444830841472*x^18/18! +...
such that C(x)^2 = 1 + S(x)^2.
D(x)^2 = 1 + 4*x^3/3! + 40*x^5/5! + 160*x^6/6! + 364*x^7/7! + 11200*x^8/8! + 24080*x^9/9! + 519120*x^10/10! + 5344724*x^11/11! + 27288800*x^12/12! + 752580920*x^13/13! + 5142016880*x^14/14! + 86718961084*x^15/15! + 1483995676800*x^16/16! + 13774998062560*x^17/17! + 356032443815440*x^18/18! +...
such that D(x)^2 = S'(x)/C(x) = C'(x)/S(x).
S(x)^3 = 6*x^3/3! + 60*x^5/5! + 360*x^6/6! + 546*x^7/7! + 23520*x^8/8! + 69720*x^9/9! + 1060920*x^10/10! + 14669886*x^11/11! + 67692240*x^12/12! + 1957699380*x^13/13! + 16377040680*x^14/14! + 228086752026*x^15/15! + 4642872212160*x^16/16! + 43205148425040*x^17/17! + 1084693228559640*x^18/18! +...
such that D(x)^3 = 1 + S(x)^3.
C(x) + S(x) = 1 + x + x^2/2! + x^3/3! + 5*x^4/4! + 21*x^5/5! + 101*x^6/6! + 581*x^7/7! + 3605*x^8/8! + 29141*x^9/9! + 239701*x^10/10! + 2205861*x^11/11! + 22832005*x^12/12! + 246573061*x^13/13! + 2990463301*x^14/14! + 38108222341*x^15/15! + 518783617205*x^16/16! + 7633121129781*x^17/17! + 116869543894901*x^18/18! + 1918479435194021*x^19/19! + 33025793008567205*x^20/20! + 595507639576003301*x^21/21! +...
such that C(x) + S(x) = exp( Integral D(x)^2 dx ).
1/(D(x) - S(x)) = 1 + x + 2*x^2/2! + 5*x^3/3! + 20*x^4/4! + 81*x^5/5! + 452*x^6/6! + 2765*x^7/7! + 19460*x^8/8! + 156121*x^9/9! + 1368052*x^10/10! + 13327125*x^11/11! + 141326500*x^12/12! + 1616350561*x^13/13! + 20040895252*x^14/14! + 264759181085*x^15/15! + 3740415315140*x^16/16! + 56164918735401*x^17/17! + 891038080096052*x^18/18! + 14957788277468645*x^19/19! + 263869908657105380*x^20/20! + 4889789934063374641*x^21/21! +...
such that 1/(D(x) - S(x)) = exp( Integral (D(x) + S(x)) * C(x) dx.
PROG
(PARI) {a(n) = my(S=x, C=1, D=1); for(i=1, n, S = intformal( C*D^2 + x*O(x^n)); C = 1 + intformal( S*D^2 ); D = 1 + intformal( C*S^2 )); n!*polcoeff(C, n)}
for(n=0, 30, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jan 06 2017
STATUS
approved