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%I #16 May 23 2016 08:06:11
%S 0,1,4,25,4,81,25,121,16,9,81,361,25,441,225,121,16,1089,36,625,81,
%T 169,361,1521,49,25,841,441,225,3721,121,2025,64,529,1089,4489,36,
%U 2401,1225,625,81,5329,169,2809,11449,361,5929,1521,6241,49,100,6561,841,6889
%N Smallest square that begins with n (in binary).
%D Allan C. Wechsler, posting to math-fun mailing list May 22 2016.
%H Chai Wah Wu, <a href="/A272680/b272680.txt">Table of n, a(n) for n = 0..10000</a>
%e a(10)=81, because 81 = 9^2 = 1010001_2 begins with 1010 = 10_2.
%o (Python)
%o from gmpy2 import isqrt
%o def A272680(n):
%o if n == 0:
%o return 0
%o else:
%o d, nd = 1, n
%o while True:
%o x = (isqrt(nd-1)+1)**2
%o if x < nd+d:
%o return int(x)
%o d *= 2
%o nd *= 2 # _Chai Wah Wu_, May 22 2016
%Y Cf. A007088, A018851, A018796, A272679, A272681.
%K nonn,base,easy
%O 0,3
%A _N. J. A. Sloane_, May 22 2016
%E More terms from _Chai Wah Wu_, May 22 2016
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