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

 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.

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