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 A123489 a(n) = Sum_{k=0..p-1} Kronecker(4k^3+1, p) where p is the n-th prime of the form 3k+1. 1
 1, -5, 7, 4, -11, -8, 1, -5, 7, -17, 19, 13, -2, -20, -23, 19, -14, 25, 7, -23, -11, 13, 28, 22, -17, -29, -26, -32, 16, -35, 1, -5, 37, -35, 13, -29, 34, 31, 19, -2, 28, 10, -23, 25, -32, 43, -29, 1, 31, -11, -26, 49, -47, -17, 43, 40, 49, 37, -8, -53, -44, -50, 16, -41, -29, 49, 31, -56, -5, 7, -35, 13, -59, -47 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Given a prime p == 1 (mod 3), the sum x is the unique solution to 4*p = x^2 + 27*y^2 where x == 1 (mod 3) and y is an integer. REFERENCES L. E. Dickson, History of the Theory of Numbers. Carnegie Institute Public. 256, Washington, DC, Vol. 1, 1919; Vol. 2, 1920; Vol. 3, 1923, see vol. 3, p. 55. LINKS EXAMPLE If p = 37, then 4*37 = (-11)^2 +27*(1)^2 where -11 = Sum_{k=0..36} Kronecker(4k^3+1, 37) and 37 is the 5th prime of the form 3k+1 so a(5) = -11. PROG (PARI) {a(n)= local(p, c); if(n<1, 0, c=0; p=0; while(c

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Last modified April 10 09:20 EDT 2021. Contains 342845 sequences. (Running on oeis4.)