A076520 n appears once if n is the sum of 2 nonzero squares in 1 way, twice if n is the sum of 2 squares in 2 ways, 3 times if n is the sum of 2 squares 3 ways etc.

2, 5, 5, 8, 10, 10, 13, 13, 17, 17, 18, 20, 20, 25, 25, 26, 26, 29, 29, 32, 34, 34, 37, 37, 40, 40, 41, 41, 45, 45, 50, 50, 50, 52, 52, 53, 53, 58, 58, 61, 61, 65, 65, 65, 65, 68, 68, 72, 73, 73, 74, 74, 80, 80, 82, 82, 85, 85, 85, 85, 89, 89, 90, 90, 97, 97, 98, 100, 100

Offset

1,1

Links

Table of n, a(n) for n=1..69.

Index entries for sequences related to sums of squares

Formula

Does limit n -> infinity a(n)/n exist?

Answer: Yes, and it is equal to 4/Pi. - Charles R Greathouse IV, Dec 01 2013

Prog

(PARI) lista(nn) = for (n=1, nn, for (i=1, n-1, if (issquare(i) && issquare(n-i), print1(n, ", ")))) \\ Michel Marcus, Nov 30 2013
(PARI) list(lim)=my(v=List()); for(n=2, lim, for(k=1, sqrtint(n-1), if(issquare(n-k^2), listput(v, n)))); Vec(v) \\ Charles R Greathouse IV, Dec 01 2013

Crossrefs

Cf. A000404, A001105, A025285, A025302.

Sequence in context: A153162 A168199 A251736 * A014249 A168071 A361861

Adjacent sequences: A076517 A076518 A076519 * A076521 A076522 A076523

Keyword

nonn

Author

Benoit Cloitre, Nov 09 2002

Extensions

Typo in definition corrected by Michel Marcus, Dec 01 2013

Status

approved