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A337188
a(n) = determinant([a(n-1), a(n-2); a(n-4), a(n-3)]) for n >= 5, a(n) = n otherwise.
0
1, 2, 3, 4, 5, 7, 13, 37, 194, 2263, 81209, 15670815, 35447299799, 2878604306322646, 45110072663945746399499, 1599030269628449375351280360624211, 4602975420092714513333476912306224941820648781605
OFFSET
1,2
REFERENCES
B. Muslu, Sayılar ve Bağlantılar, Luna, 2021, pp. 18-22.
FORMULA
a(n) = a(n-1)*a(n-3) - a(n-2)*a(n-4) for n >= 5, a(n) = n for n <= 4.
MAPLE
a:= proc(n) option remember; `if`(n<5, n,
a(n-1)*a(n-3)-a(n-2)*a(n-4))
end:
seq(a(n), n=1..18); # Alois P. Heinz, Jan 29 2021
MATHEMATICA
a[n_] := a[n] = If[n < 5, n, Det @ Map[a, n - {{1, 2}, {4, 3}}, {2}]]; Array[a, 20] (* Amiram Eldar, Jan 29 2021 *)
nxt[{a_, b_, c_, d_}]:={b, c, d, Det[{{d, c}, {a, b}}]}; NestList[nxt, {1, 2, 3, 4}, 20][[All, 1]] (* Harvey P. Dale, Oct 23 2022 *)
PROG
(PARI) a(n) = if (n<=4, n, a(n-1)*a(n-3) - a(n-2)*a(n-4)); \\ Michel Marcus, Jan 29 2021
CROSSREFS
Sequence in context: A066661 A268199 A178767 * A125707 A039060 A278442
KEYWORD
nonn
AUTHOR
Burak Muslu, Jan 29 2021
STATUS
approved