OFFSET
0,8
COMMENTS
Inspired by Somos-7 sequence.
a(n) is integer for n >= 0.
a(n+1)/a(n) is integer for n >= 0.
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..18
FORMULA
a(n) * a(n-7) = a(n-1) * a(n-6) + a(n-1) * a(n-2) * a(n-5) * a(n-6) + a(n-1) * a(n-2) * a(n-3) * a(n-4) * a(n-5) * a(n-6).
a(6-n) = a(n).
Let b(n) = b(n-6) * (b(n-2) * b(n-3) * b(n-4) * (b(0) * b(1) * ... * b(n-5))^2 * (b(n-3) * (b(0) * b(1) * ... * b(n-4))^2 + 1)+ 1) with b(0) = b(1) = b(2) = b(3) = b(4) = b(5) = 1, then a(n) = a(n-1) * b(n-1) = b(0) * b(1) * ... * b(n-1) for n > 0.
EXAMPLE
a(7) = a(6) * b(6) = 1 * 3 = 3,
a(8) = a(7) * b(7) = 3 * 3 = 9,
a(9) = a(8) * b(8) = 9 * 7 = 63,
a(10) = a(9) * b(9) = 63 * 37 = 2331.
PROG
(Ruby)
def A(k, n)
a = Array.new(2 * k + 1, 1)
ary = [1]
while ary.size < n + 1
i = 0
k.downto(1){|j|
i += 1
i *= a[j] * a[-j]
}
break if i % a[0] > 0
a = *a[1..-1], i / a[0]
ary << a[0]
end
ary
end
def A276535(n)
A(3, n)
end
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 16 2016
STATUS
approved