The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A170991 Number of genus 2, degree n, simply ramified covers of an elliptic curve. 8
 2, 16, 60, 160, 360, 672, 1240, 1920, 3180, 4400, 6832, 8736, 12880, 15840, 22320, 26112, 36666, 41040, 55720, 62720, 82104, 89056, 119520, 124800, 161980, 174240, 219744, 227360, 295920, 297600, 377952, 392832, 480420, 486080, 623820, 607392, 753160, 771680, 934800, 918400, 1157184 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS The reference gives a generating function and the terms up to degree 18. LINKS Table of n, a(n) for n=2..42. Mike Roth and Noriko Yu, Mirror Symmetry for Elliptic Curves: The A-Model (Fermionic) Counting, Clay Mathematics Proceedings, Volume 11, 2010. FORMULA G.f.: (5*E_2^3 - 3*E_2*E_4 - 2*E_6)/25920, where E_k = 1 - (2*k/B_k)*Sum_{i > 0} Sum_{d dividing i} d^(k-1)*q^i is the Eisenstein series of weight k. - Robin Visser, Aug 08 2023 PROG (Sage) def a(n): E2 = sum([1]+[-24*sigma(k)*x^k for k in range(1, n+1)]) E4 = sum([1]+[240*sigma(k, 3)*x^k for k in range(1, n+1)]) E6 = sum([1]+[-504*sigma(k, 5)*x^k for k in range(1, n+1)]) f = (5*E2^3 - 3*E2*E4 - 2*E6)/25920 return f.taylor(x, 0, n).coefficient(x^n) # Robin Visser, Aug 08 2023 CROSSREFS Cf. A170992, A170993, A170994, A170995, A170996, A170997, A170998, A170999. Sequence in context: A293620 A206980 A357816 * A209219 A207688 A208495 Adjacent sequences: A170988 A170989 A170990 * A170992 A170993 A170994 KEYWORD nonn AUTHOR N. J. A. Sloane, Aug 31 2010 EXTENSIONS More terms from Robin Visser, Aug 08 2023 STATUS approved

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

Last modified May 20 03:01 EDT 2024. Contains 372703 sequences. (Running on oeis4.)