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A017921
Powers of sqrt(5) rounded up.
3
1, 3, 5, 12, 25, 56, 125, 280, 625, 1398, 3125, 6988, 15625, 34939, 78125, 174693, 390625, 873465, 1953125, 4367321, 9765625, 21836602, 48828125, 109183007, 244140625, 545915034, 1220703125, 2729575168
OFFSET
0,2
LINKS
EXAMPLE
sqrt(5)^3 = 11.18033988749895... so a(3) = 12.
sqrt(5)^4 = 25, so a(4) = 25.
sqrt(5)^5 = 55.90169943749474241... so a(5) = 56.
MATHEMATICA
Ceiling[Sqrt[5]^Range[0, 40]] (* Vincenzo Librandi, Nov 20 2011 *)
PROG
(Magma) [Ceiling(Sqrt(5^n)): n in [0..40]]; // Vincenzo Librandi, Nov 20 2011
(PARI) a(n) = ceil(sqrt(5^n)); \\ Michel Marcus, Dec 14 2017
(Python)
from math import isqrt
def A017921(n): return isqrt(5**n)+(n&1) # Chai Wah Wu, Jun 19 2024
CROSSREFS
Sequence in context: A129757 A135019 A141685 * A280000 A241097 A267725
KEYWORD
nonn,easy
STATUS
approved