login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A174400 Hankel transform of A174399. 3
1, 0, -1, -1, -1, -2, -1, 3, 7, 8, 25, 37, -47, -318, -559, -2023, -7039, 496, 90431, 314775, 1139599, 8007614, 13512079, -154788437, -1247862041, -5097732072, -56844671623, -290379801907, 1403230649825, 32188159859842 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

Essentially a (1,-1) Somos-4 sequence.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..150

FORMULA

a(n) = (a(n-1)*a(n-3) - a(n-2)^2)/a(n-4), n>=6.

a(n) = -a(2-n), a(n)*a(n+5) = a(n+1)*a(n+4) - 2*a(n+2)*a(n+3) for all n in Z. - Michael Somos, Sep 26 2018

MATHEMATICA

nxt[{a_, b_, c_, d_}]:={b, c, d, (d*b-c^2)/a}; Join[{1, 0}, NestList[nxt, {-1, -1, -1, -2}, 30][[All, 1]]] (* Harvey P. Dale, Sep 07 2017 *)

Join[{1, 0}, RecurrenceTable[{a[n] == (a[n-1]*a[n-3] -a[n-2]^2)/a[n-4], a[2] == -1, a[3] == -1, a[4] == -1, a[5] == -2}, a, {n, 2, 50}]] (* G. C. Greubel, Sep 25 2018 *)

PROG

(PARI) m=20; v=concat([-1, -1, -1, -2], vector(m-4)); for(n=5, m, v[n] = ( 100*v[n-1]*v[n-3] - 196*v[n-2]^2)/v[n-4]); concat([1, 0], v) \\ G. C. Greubel, Sep 25 2018

(Magma) I:=[-1, -1, -1, -2]; [1, 0] cat [n le 4 select I[n] else (Self(n-1)*Self(n-3) - Self(n-2)^2)/Self(n-4): n in [1..20]]; // G. C. Greubel, Sep 25 2018

CROSSREFS

Sequence in context: A201615 A033640 A112027 * A178079 A258987 A174254

Adjacent sequences: A174397 A174398 A174399 * A174401 A174402 A174403

KEYWORD

easy,sign

AUTHOR

Paul Barry, Mar 18 2010

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 2 10:29 EST 2022. Contains 358493 sequences. (Running on oeis4.)