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

Author

Benoit Cloitre, Nov 09 2002

Keywords

• nonn

Links

• Index entries for sequences related to sums of squares

Crossrefs

Cf. A000404, A001105, A025285, A025302.

Programs

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

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

Extensions

Typo in definition corrected by Michel Marcus, Dec 01 2013