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%I #19 May 23 2016 08:04:55
%S 0,1,2,5,2,9,5,11,4,3,9,19,5,21,15,11,4,33,6,25,9,13,19,39,7,5,29,21,
%T 15,61,11,45,8,23,33,67,6,49,35,25,9,73,13,53,107,19,77,39,79,7,10,81,
%U 29,83,59,21,15,43,61,87,11,89,63,45,8,129,23,93,33,47
%N a(n)^2 is the smallest square whose binary expansion begins with the binary expansion of n.
%D Allan C. Wechsler, posting to math-fun mailing list May 22 2016.
%H Chai Wah Wu, <a href="/A272679/b272679.txt">Table of n, a(n) for n = 0..10000</a>
%e a(10)=9, because 9^2 = 81 = 1010001_2 begins with 1010 = 10_2.
%o (Python)
%o from gmpy2 import isqrt
%o def A272679(n):
%o if n == 0:
%o return 0
%o else:
%o d, nd = 1, n
%o while True:
%o x = isqrt(nd-1)+1
%o if x**2 < nd+d:
%o return int(x)
%o d *= 2
%o nd *= 2 # _Chai Wah Wu_, May 22 2016
%Y Cf. A007088, A018851, A018796, A272680, 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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