A276268 a(0) = a(1) = a(2) = a(3) = 1; for n>3, a(n) = ( a(n-1)*a(n-2)*a(n-3) + 1 )^2 / a(n-4).

1, 1, 1, 1, 4, 25, 10201, 1040606050201, 17606710134796383100801078407630169, 1397251576763829044923817239566095383950667477080314561212188721224520791793149263311589905001958916

Offset

0,5

Links

Seiichi Manyama, Table of n, a(n) for n = 0..11

Formula

a(n) = A276267(n)^2.

Mathematica

RecurrenceTable[{a[n] == (a[n - 1] a[n - 2] a[n - 3] + 1)^2/a[n - 4], a[0] == a[1] == a[2] == a[3] == 1}, a, {n, 0, 10}] (* Michael De Vlieger, Aug 26 2016 *)
nxt[{a_, b_, c_, d_}]:={b, c, d, (b*c*d+1)^2/a}; NestList[nxt, {1, 1, 1, 1}, 10][[All, 1]] (* Harvey P. Dale, Jan 31 2020 *)

Prog

(Ruby)
def A(m, n)
  a = Array.new(m, 1)
  ary = [1]
  while ary.size < n + 1
    i = a[1..-1].inject(:*) + 1
    i *= i
    break if i % a[0] > 0
    a = *a[1..-1], i / a[0]
    ary << a[0]
  end
  ary
end
def A276268(n)
  A(4, n)
end

Crossrefs

Cf. A081068, A276266, A276267.

Sequence in context: A284106 A063802 A276266 * A350081 A350080 A306687

Adjacent sequences: A276265 A276266 A276267 * A276269 A276270 A276271

Keyword

nonn

Author

Seiichi Manyama, Aug 26 2016

Status

approved