The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A127310 a(n) = |E(GF(p))| = number of rational points on the elliptic curve E: y^2 + y = x^3 - x^2 mod p where the prime p is p(n) or p(n+1) according as n < 5 or n >= 5. 2
 5, 5, 5, 10, 10, 20, 20, 25, 30, 25, 35, 50, 50, 40, 60, 55, 50, 75, 75 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS E is singular over GF(p(5)) = GF(11) so we take p != 11. In other words, p runs through the primes other than 11. Hasse proved that |a(n) - (p+1)| <= 2*sqrt(p) where p is p(n) or p(n+1) according as n < 5 or n >= 5. Elkies proved that a(n) = p(n+1) + 1 for infinitely many n. a(n) is divisible by 5 because the points oo, (0,0), (0,-1), (1,0), (1,-1) on E form a subgroup of E(GF(p)) of order 5. REFERENCES N. Koblitz, Introduction to Elliptic Curves and Modular Forms. New York: Springer-Verlag, 1993. B. Mazur, The Structure of Error Terms in Number Theory and an Introduction to the Sato-Tate Conjecture, Current Events Bulletin, Amer. Math. Soc., 2007. B. Mazur, Finding meaning in error terms, Bull. Amer. Math. Soc., 45 (No. 2, 2008), 185-228. J. H. Silverman, The Arithmetic of Elliptic Curves, Graduate Texts in Math., vol. 106, Springer-Verlag, Berlin and New York, 1986. LINKS FORMULA a(n) ~ p(n+1) + 1 as n -> oo. a(n) = p+1 - b(p) where q*Prod(k=1 to oo, ((1 - q^k)(1 - q^11k))^2) = Sum(k=1 to oo, b(k)*q^k) and p is p(n) or p(n+1) according as n < 5 or n >= 5. EXAMPLE q*Prod(k=1 to oo, ((1 - q^k)(1 - q^11k))^2) = q - 2q^2 - q^3 + ..., so a(1) = p(1) + 1 - b(p(1)) = 2 + 1 - b(2) = 3 - (-2) = 5 and a(2) = p(2) + 1 - b(p(2)) = 3 + 1 - b(3) = 4 - (-1) = 5. CROSSREFS a(n) = 5*A127311(n). Cf. A000594, A127309. Sequence in context: A194428 A299695 A135089 * A214925 A101597 A119991 Adjacent sequences:  A127307 A127308 A127309 * A127311 A127312 A127313 KEYWORD nonn,more AUTHOR Jonathan Sondow, Jan 12 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 27 03:08 EDT 2020. Contains 337380 sequences. (Running on oeis4.)