This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A000662 Relations with 3 arguments on n nodes. (Formerly M2180 N0872) 7
 2, 136, 22377984, 768614354122719232, 354460798875983863749270670915141632, 146267071761884981524915186989628577728537526896649216991428608 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES F. Bergeron, G. Labelle and P. Leroux, Combinatorial Species and Tree-Like Structures, Cambridge, 1998, p. 76 (2.2.31) W. Oberschelp, Kombinatorische Anzahlbestimmungen in Relationen, Math. Ann., 174 (1967), 53-78. 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 Alois P. Heinz, Table of n, a(n) for n = 1..15 P. J. Cameron, Sequences realized by oligomorphic permutation groups, J. Integ. Seqs. Vol. 3 (2000), #00.1.5. W. Oberschelp, Strukturzahlen in endlichen Relationssystemen, in Contributions to Mathematical Logic (Proceedings 1966 Hanover Colloquium), pp. 199-213, North-Holland Publ., Amsterdam, 1968. [Annotated scanned copy] 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, ...] = 2^sum_{i, j, k>=1} (i*j*k*s_i*s_j*s_k/lcm(i, j, k)). CROSSREFS Cf. A000595, A001377, A051241. Sequence in context: A226118 A216030 A216083 * A139907 A195379 A221227 Adjacent sequences:  A000659 A000660 A000661 * A000663 A000664 A000665 KEYWORD nonn,nice AUTHOR EXTENSIONS Formula from 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 March 18 20:24 EDT 2019. Contains 321294 sequences. (Running on oeis4.)