This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A001330 Number of n-element algebras with 2 binary operations. (Formerly M5398 N2346) 0
 1, 1, 136, 64573605, 768614338015543296, 740148683083442627372862307855625, 147760220727384062234340471228346859265417269763446784, 13097167596472133103922286145973062271265962292695709182416029922453889335720758 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Isomorphisms classes of a set A with two functions f1,f2: A X A -> A. REFERENCES M. A. Harrison, The number of isomorphism types of finite algebras, Proc. Amer. Math. Soc., 17 (1966), 731-737. N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS FORMULA a(n) = sum {1*s_1+2*s_2+...=n} (fix A[s_1, s_2, ...]/(1^s_1*s_1!*2^s_2*s_2!*...)) where fix A[s_1, s_2, ...] = Product_{i, j>=1} ( (sum {d|lcm(i, j)} (d*s_d))^(gcd(i, j)*s_i*s_j*2)). a(n) is asymptotic to n^(2*n^2)/n! = A008972(n)/A000142(n). CROSSREFS Cf. A001329, A001331. Sequence in context: A233127 A157880 A233254 * A091510 A134885 A259680 Adjacent sequences:  A001327 A001328 A001329 * A001331 A001332 A001333 KEYWORD nonn AUTHOR EXTENSIONS Edited and extended with formula by Christian G. Bower, Jan 06 2004 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 January 23 17:24 EST 2019. Contains 319399 sequences. (Running on oeis4.)