login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A289068 Recurrence a(n+2) = Sum_{k=0..n} binomial(n,k)a(k)a(n+1-k) with a(0)=1, a(1)=-2. 15
1, -2, -2, 2, 14, 10, -170, -670, 2270, 30490, 26950, -1435150, -8513650, 59564650, 1050090550, 486517250, -113618013250, -831340535750, 10136160835750, 208459859695250, -121723298991250, -41568491959973750, -338549875950886250, 6637158567781561250 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

One of a family of integer sequences whose e.g.f.s satisfy the differential equation f''(z) = f'(z)f(z). For more details, see A289064.

LINKS

Stanislav Sykora, Table of n, a(n) for n = 0..200

S. Sykora, Sequences related to the differential equation f'' = af'f, Stan's Library, Vol. VI, Jun 2017.

FORMULA

E.g.f.: -sqrt(5)*tanh(z*sqrt(5)/2 - acosh(sqrt(5)/2)).

E.g.f. for the sequence (-1)^(n+1)*a(n): -sqrt(5)*tanh(z*sqrt(5)/2 + acosh(sqrt(5)/2)).

PROG

(PARI) c0=1; c1=-2; nmax = 200;

  a=vector(nmax+1)); a[1]=c0; a[2]=c1;

  for(m=0, #a-3, a[m+3]=sum(k=0, m, binomial(m, k)*a[k+1]*a[m+2-k]));

  a

(Python)

from sympy import binomial

l=[1, -2]

for n in xrange(2, 51): l+=[sum([binomial(n - 2, k)*l[k]*l[n - 1 - k] for k in xrange(n - 1)]), ]

print l # Indranil Ghosh, Jun 30 2017

CROSSREFS

Sequences for other starting pairs: A000111 (1,1), A289064 (1,-1), A289065 (2,-1), A289066 (3,1), A289067 (3,-1), A289069 (3,-2), A289070 (0,3).

Sequence in context: A077991 A049148 A183584 * A063898 A074052 A129409

Adjacent sequences:  A289065 A289066 A289067 * A289069 A289070 A289071

KEYWORD

sign

AUTHOR

Stanislav Sykora, Jun 23 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified September 26 10:52 EDT 2017. Contains 292518 sequences.