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A256858
a(n) = (-a(n-1) * a(n-6) + a(n-2) * a(n-5)) / a(n-7) with a(n) = 1 if abs(n) < 4, a(11) = 4.
3
1, 1, 1, 1, 0, 1, -1, 2, -3, 3, -3, 4, -2, 8, 9, 17, 29, 50, 83, 107, 56, 239, -243, 1103, -2351, 3775, -7227, 14463, -18648, 55283, 54011, 256666, 698301, 2059753, 5324929, 9820288, 15128062, 55075036, -28437275, 503857819, -1438167267, 4083736906
OFFSET
0,8
COMMENTS
Similar to the Somos-6 and Somos-7 sequences with many bilinear identities.
LINKS
FORMULA
a(2*n - 5) = A102276(n) for all n in Z.
a(2*n) = A256916(n) for all n in Z.
a(n) = a(-n) for all n in Z.
0 = a(n) * a(n+7) + a(n+1) * a(n+6) - a(n+2) * a(n+5) for all n in Z.
0 = a(n) * a(n+8) - a(n+2) * a(n+6) - a(n+4)^2 + (2 - mod(n,2)) * a(n+3) * a(n+5) for all n in Z.
0 = a(n) * a(n+11) + a(n+1) * a(n+10) + a(n+5) * a(n+6) for all n in Z. - Michael Somos, Apr 14 2015
MATHEMATICA
Join[{1, 1, 1, 1, 0, 1, -1, 2, -3, 3, -3, 4}, RecurrenceTable[{a[n] == (-a[n - 1]*a[n - 6] + a[n - 2]*a[n - 5])/a[n - 7], a[12] == -2, a[13] == 8, a[14] == 9, a[15] == 17, a[16] == 29, a[17] == 50, a[18] == 83}, a, {n, 12, 60}]] (* G. C. Greubel, Aug 03 2018 *)
a[n_] := Which[n<0, a[-n], n<12, {1, 1, 1, 1, 0, 1, -1, 2, -3, 3, -3, 4}[[1+n]], True, a[n] = (-a[n-1]*a[n-6] + a[n-2]*a[n-5])/a[n-7]]; (* Michael Somos, Dec 16 2023 *)
PROG
(PARI) {a(n) = my(an); n = abs(n)+1; an = concat([ 1, 1, 1, 1, 0, 1, -1, 2, -3, 3, -3, 4], vector(max(0, n-12), k)); for(k=13, n, an[k] = (-an[k-1] * an[k-6] + an[k-2] * an[k-5]) / an[k-7]); an[n]};
(PARI) {a(n) = my(an); n = abs(n)+1; an = vector(n, k, 1); if( n>=5, an[5] = 0); if( n>=7, an[7] = -1); if( n>=8, an[8] = 2); for(k=9, n, an[k] = if( k==12, 4, (-an[k-1] * an[k-6] + an[k-2] * an[k-5]) / an[k-7])); an[n]};
(Magma) I:=[-2, 8, 9, 17, 29, 50, 83]; [1, 1, 1, 1, 0, 1, -1, 2, -3, 3, -3, 4] cat [n le 7 select I[n] else (-Self(n-1)*Self(n-6) + Self(n-2)*Self(n-5))/Self(n-7): n in [1..30]]; // G. C. Greubel, Aug 03 2018
CROSSREFS
Sequence in context: A089335 A088093 A282352 * A049837 A326202 A322988
KEYWORD
sign
AUTHOR
Michael Somos, Apr 12 2015
STATUS
approved