A229766 -id:A229766 - cp's OEIS frontend

A229687 Odd squares whose binary reversal is also a square.

1, 9, 20457529, 143784081, 331130809, 4365905625, 5216450625, 20074072489, 1193532215121, 10036851273801, 36014509461681, 38767247532225, 41413201925481, 155991531977649, 320642706437001, 2543173099393689, 2696589987547401, 4665141483989281, 87463589042698969

Offset: 1

Alex Ratushnyak, Dec 19 2013

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, ...

A029983 is a subsequence (after zero). - Antti Karttunen, Dec 20 2013

Cf. A000290, A029983, A074832, A229766.

#include 
#include 
int main() {
  unsigned long long n, t, r, sr;
  for (n=1; n<(1ULL<<32); n+=2) {
     t = n*n;
     r = 0;
     while (t)  r = r*2+(t&1),  t >>= 1;
     sr = sqrt(r);
     if (sr*sr==r)  printf("%llu, ", n*n);
  }
  return 0;
}

(define (A229687 n) (A000290 (A229766 n))) ;; Antti Karttunen, Dec 20 2013

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

cp's OEIS Frontend

A229687 Odd squares whose binary reversal is also a square.

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