The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 60, we have over 367,000 sequences, and we’ve crossed 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS Table of n, a(n) for n=0..19. 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 Adjacent sequences: A028495 A028496 A028497 * A028499 A028500 A028501 KEYWORD nonn AUTHOR Florian Lengyel (flengyel(AT)email.gc.cuny.edu) EXTENSIONS More terms from Sean A. Irvine, Feb 03 2020 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 December 1 23:26 EST 2023. Contains 367503 sequences. (Running on oeis4.)