A027662 a(n)/1000 gives sqrt(n) to 3 places after the decimal point.
1000, 1414, 1732, 2000, 2236, 2449, 2646, 2828, 3000, 3162, 3317, 3464, 3606, 3742, 3873, 4000, 4123, 4243, 4359, 4472, 4583, 4690, 4796, 4899, 5000, 5099, 5196, 5292, 5385, 5477, 5568, 5657, 5745, 5831, 5916, 6000, 6083, 6164, 6245, 6325, 6403, 6481, 6557, 6633
Offset: 1
Programs
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Maple
lprint(round(evalf(1000*sqrt(n))));
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Mathematica
Table[Floor[1000*Sqrt[n]+1/2],{n,40}] (* Harvey P. Dale, Apr 22 2011 *) -
Python
from math import isqrt def A027662(n): return (m:=isqrt(k:=n*10**6))+int((k-m*(m+1)<<2)>=1) # Chai Wah Wu, Jul 30 2022