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A090735
Number of positive squarefree numbers <= n that can be expressed as a sum of 2 squares > 0.
3
0, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 15, 16, 16, 16, 16, 16, 16, 16, 16, 17, 17
OFFSET
1,5
REFERENCES
Steven R. Finch, Mathematical Constants, Cambridge, 2003, p. 100
LINKS
FORMULA
a(n) is asymptotic to (6K/Pi^2)*n/sqrt(log(n)) where K is the Landau-Ramanujan constant (A064533).
MATHEMATICA
Accumulate[Table[Boole[n > 1 && SquareFreeQ[n] && AllTrue[FactorInteger[n][[;; , 1]], Mod[#, 4] < 3 &]], {n, 1, 100}] ] (* Amiram Eldar, May 08 2022 *)
PROG
(PARI) a(n)=sum(i=1, n, issquarefree(i)*if(sum(u=1, i, sum(v=1, u, if(u^2+v^2-i, 0, 1))), 1, 0))
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Jan 18 2004
STATUS
approved