A017968 Powers of sqrt(21) rounded to nearest integer.
1, 5, 21, 96, 441, 2021, 9261, 42439, 194481, 891224, 4084101, 18715702, 85766121, 393029742, 1801088541, 8253624572, 37822859361, 173326116021, 794280046581, 3639848436450, 16679880978201, 76436817165460, 350277500542221, 1605173160474663, 7355827511386641
Offset: 0
Keywords
Links
- Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Programs
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Magma
[Round(Sqrt(21)^n): n in [0..30]]; // Vincenzo Librandi, Nov 20 2011
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Maple
a:= n-> round(sqrt(21)^n): seq(a(n), n=0..25); # Alois P. Heinz, Jul 29 2022
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Mathematica
Floor[(Sqrt[21])^Range[0,25]+1/2] (* Harvey P. Dale, Sep 22 2011 *)
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PARI
a(n)=round(sqrt(21)^n) \\ Charles R Greathouse IV, Nov 18 2011
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Python
from math import isqrt def A017968(n): return (m:=isqrt(k:=21**n))+int((k-m*(m+1)<<2)>=1) # Chai Wah Wu, Jul 29 2022