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 A094572 Number of pairs of integers x, y (of either sign) with x^2 - y^2 = n. 5
 2, 0, 4, 2, 4, 0, 4, 4, 6, 0, 4, 4, 4, 0, 8, 6, 4, 0, 4, 4, 8, 0, 4, 8, 6, 0, 8, 4, 4, 0, 4, 8, 8, 0, 8, 6, 4, 0, 8, 8, 4, 0, 4, 4, 12, 0, 4, 12, 6, 0, 8, 4, 4, 0, 8, 8, 8, 0, 4, 8, 4, 0, 12, 10, 8, 0, 4, 4, 8, 0, 4, 12, 4, 0, 12, 4, 8, 0, 4, 12, 10, 0, 4, 8, 8, 0, 8, 8, 4, 0, 8, 4, 8, 0, 8, 16, 4, 0, 12, 6 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The old entry with this sequence number was a duplicate of A058071. REFERENCES M. N. Huxley, Area, Lattice Points and Exponential Sums, Oxford, 1996; p. 236. LINKS Ray Chandler, Table of n, a(n) for n = 1..10000 N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references) FORMULA a(n) = 2d(n) if n is odd, = 2d(n/4) if n == 0 mod 4, otherwise 0, where d() = A000005(). a(n) = 2 * A112329(n). - Ray Chandler, Aug 23 2014 MAPLE with(numtheory); f:=proc(n) if n mod 2 = 1 then RETURN(2*tau(n)); fi; if n mod 4 = 0 then RETURN(2*tau(n/4)); fi; 0; end; MATHEMATICA Table[If[OddQ[n], 2DivisorSigma[0, n], If[OddQ[n/2], 0, 2DivisorSigma[0, n/4]]], {n, 100}] (* Ray Chandler, Aug 23 2014 *) CROSSREFS Cf. A000005, A093061, A112329. Sequence in context: A155984 A028609 A107490 * A323905 A079534 A229910 Adjacent sequences:  A094569 A094570 A094571 * A094573 A094574 A094575 KEYWORD nonn AUTHOR N. J. A. Sloane, Nov 02 2008 STATUS approved

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Last modified February 20 13:20 EST 2020. Contains 332077 sequences. (Running on oeis4.)