OFFSET
1,3
COMMENTS
a(n)/a(n-1) ~ cube root of 2.
a(n)/a(n-3) ~ 2.
EXAMPLE
a(12) = ceiling(sqrt(2*a(11)*a(10))) = ceiling(sqrt(2*15*12)) = ceiling(sqrt(360)) = 19.
MATHEMATICA
a[n_] := a[n] = If[n<3, 1, Ceiling[Sqrt[2 a[n-1] a[n-2]]]]; Array[a, 50] (* Giovanni Resta, Nov 26 2019 *)
RecurrenceTable[{a[1]==a[2]==1, a[n]==Ceiling[Sqrt[2a[n-1]a[n-2]]]}, a, {n, 50}] (* Harvey P. Dale, Apr 13 2020 *)
PROG
(Python)
import math
r = []
r.append(1)
r.append(1)
i = 2
while i < 1001:
r.append(math.ceil(math.sqrt(2*r[i-1]*r[i-2])))
i += 1
print(r)
CROSSREFS
KEYWORD
nonn
AUTHOR
Oren Meisner, Aug 14 2018
STATUS
approved