A017921 Powers of sqrt(5) rounded up.

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

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

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

Cf. A017919, A017920.

Sequence in context: A129757 A135019 A141685 * A280000 A241097 A267725

Adjacent sequences: A017918 A017919 A017920 * A017922 A017923 A017924

Keyword

nonn,easy

Author

N. J. A. Sloane

Status

approved