A127912 Number of nonisomorphic disconnected mappings (or mapping patterns) from n points to themselves; number of disconnected endofunctions.

0, 1, 3, 10, 27, 79, 218, 622, 1753, 5007, 14274, 40954, 117548, 338485, 975721, 2817871, 8146510, 23581381, 68322672, 198138512, 575058726, 1670250623, 4854444560, 14117859226, 41081418963, 119606139728

Offset

0,3

Comments

Number of endofunctions on n points whose functional digraphs (with loops allowed) are nontrivially the directed sum of two or more digraphs of endofunctions.

References

Steven R. Finch, Mathematical Constants, Cambridge, 2003, Section 5.6.6.

R. A. Fisher, Contributions to Mathematical Statistics, Wiley, 1950, 41.399 and 41.401.

Links

Table of n, a(n) for n=0..25.

N. G. de Bruijn and D. A. Klarner, Multisets of aperiodic cycles, SIAM J. Algebraic Discrete Methods 3 (1982), no. 3, 359--368. MR0666861(84i:05008).

Eric Weisstein's World of Mathematics, Functional Graph.

Formula

a(n) = A001372(n) - A002861(n).

Example

a(0) = 0, as the null digraph is formally neither connected nor disconnected.
a(1) = 0, as the unique endofunction on one point is the identity function on one value and is connected.
a(2) = 1, as there are 3 endofunctions on two points, two of which are "prime endofunctions" and one of which is the direct sum of two copies of the unique endofunction on one point, namely two points-with-loops, or the identity function on two values; 3 - 2 = 1.
a(3) = A001372(3) - A002861(3) = 7 - 4 = 3.
a(4) = A001372(4) - A002861(4) = 19 - 9 = 10.
a(5) = A001372(5) - A002861(5) = 47 - 20 = 27.
a(6) = 130 - 51 = 79.
a(7) = 343 - 125 = 218.
a(8) = 951 - 329 = 622.
a(9) = 2615 - 862 = 1753.
a(10) = 7318 - 2311 = 5007.

Crossrefs

Cf. A000081, A000273, A001372, A002861, A003027, A003085, A062738, A116950, A126285, A127909-A127915.

Sequence in context: A154496 A027251 A279136 * A005956 A373279 A379297

Adjacent sequences: A127909 A127910 A127911 * A127913 A127914 A127915

Keyword

easy,nonn

Author

Jonathan Vos Post, Feb 06 2007

Status

approved