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

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Examples

			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.
		

Links

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

Crossrefs

Cf. A017919, A017920.

Programs

Magma

[Ceiling(Sqrt(5^n)): n in [0..40]]; // Vincenzo Librandi, Nov 20 2011

Mathematica

Ceiling[Sqrt[5]^Range[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