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A028498
Let [n] = {0,...,n-1}; a(n) is number of functions f:[n] -> [n] for which there exists an injection g:[n] -> [n+1] such that for j with 0 <= j < n, either g(j) = f(j) or g(j) = f(j)+1.
0
1, 4, 24, 186, 1770, 19980, 260820, 3863160, 63980280, 1171195200, 23476068000, 511296786000, 12021166357200, 303414507396000, 8182057223340000, 234753130435824000, 7139815170664176000, 229442416696164672000, 7767967204994540544000, 276345182709766890720000
OFFSET
0,2
LINKS
Ariel Halpert, Flórián Lengyel and János Pach, Cellular telephone networks and random maps in hypergraphs, Discrete Appl. Math. 103 (2000), no. 1-3, 111-126.
FORMULA
a(n) = T(n, n) where T(1, n) = n, T(2, n) = n^2, and T(m, n) = T(m, n-1) + 2*m*T(m-1, n-1) - m*T(m-1, n-2) - binomial(m, 2)*T(m-2, n-2) for 1 <= m <= n+1. - Sean A. Irvine, Feb 03 2020
CROSSREFS
Sequence in context: A271215 A135905 A239296 * A001397 A001506 A354123
KEYWORD
nonn
AUTHOR
Florian Lengyel (flengyel(AT)email.gc.cuny.edu)
EXTENSIONS
More terms from Sean A. Irvine, Feb 03 2020
STATUS
approved