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A017968
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Powers of sqrt(21) rounded to nearest integer.
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1
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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
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OFFSET
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0,2
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LINKS
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MAPLE
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a:= n-> round(sqrt(21)^n):
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MATHEMATICA
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PROG
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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
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CROSSREFS
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Bisection gives A009965 (even part).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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