A229687 - OEIS

%I #36 Dec 21 2013 03:05:46

%S 1,9,20457529,143784081,331130809,4365905625,5216450625,20074072489,

%T 1193532215121,10036851273801,36014509461681,38767247532225,

%U 41413201925481,155991531977649,320642706437001,2543173099393689,2696589987547401,4665141483989281,87463589042698969

%N Odd squares whose binary reversal is also a square.

%C The sequence of binary reversals that are squares is a permutation of a(n), it begins: 1, 9, 20457529, 143784081, 331130809, 5216450625, 4365905625, 20074072489, 1193532215121, 10036851273801, 38767247532225, 36014509461681, ...

%C A029983 is a subsequence (after zero). - _Antti Karttunen_, Dec 20 2013

%F a(n) = A229766(n)^2.

%o (C)

%o #include <stdio.h>

%o #include <math.h>

%o int main() {

%o   unsigned long long n, t, r, sr;

%o   for (n=1; n<(1ULL<<32); n+=2) {

%o      t = n*n;

%o      r = 0;

%o      while (t)  r = r*2+(t&1),  t >>= 1;

%o      sr = sqrt(r);

%o      if (sr*sr==r)  printf("%llu, ", n*n);

%o   }

%o   return 0;

%o }

%o (Scheme) (define (A229687 n) (A000290 (A229766 n))) ;; _Antti Karttunen_, Dec 20 2013

%Y Cf. A000290, A029983, A074832, A229766.

%K nonn,base

%O 1,2

%A _Alex Ratushnyak_, Dec 19 2013