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 A028244 a(n) = 4^(n-1) - 3*3^(n-1) + 3*2^(n-1) - 1 (essentially Stirling numbers of second kind). 19
 0, 0, 0, 6, 60, 390, 2100, 10206, 46620, 204630, 874500, 3669006, 15195180, 62350470, 254135700, 1030793406, 4166023740, 16792841910, 67558001700, 271392695406, 1089054420300, 4366671742950, 17498055448500, 70086339807006 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS For n>=4, a(n) is equal to the number of functions f: {1,2,...,n-1}->{1,2,3,4} such that Im(f) contains 3 fixed elements. - Aleksandar M. Janjic and Milan Janjic, Feb 27 2007 LINKS Seiichi Manyama, Table of n, a(n) for n = 1..1661 K. S. Immink, Coding Schemes for Multi-Level Channels that are Intrinsically Resistant Against Unknown Gain and/or Offset Using Reference Symbols, Electronics Letters ( Volume: 50, Issue: 1, January 2 2014 ). Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets FORMULA a(n) = 6*S(n, 4) = 6*A000453(n). - Emeric Deutsch, May 02 2004 G.f.: 6x^4/((1-x)(1-2x)(1-3x)(1-4x)). - R. J. Mathar, Oct 23 2008 E.g.f.: (exp(4*x) - 4*exp(3*x) + 6*exp(2*x) - 4*exp(x) + 1)/4, with a(0) = 0. - Wolfdieter Lang, May 03 2017 a(n) = 2*A032263(n). - Alois P. Heinz, Jan 24 2018 MATHEMATICA Table[4^(n - 1) - 3*3^(n - 1) + 3*2^(n - 1) - 1, {n, 1, 30}] (* Stefan Steinerberger, Apr 13 2006 *) Table[6*StirlingS2[n, 4], {n, 1, 30}] (* G. C. Greubel, Nov 19 2017 *) PROG (MAGMA) [4^(n-1) - 3*3^(n-1) + 3*2^(n-1) - 1: n in [1..30]]; // G. C. Greubel, Nov 19 2017 (PARI) for(n=1, 30, print1(6*stirling(n, 4, 2), ", ")) \\ G. C. Greubel, Nov 19 2017 CROSSREFS Cf. A000453, A008277, A032263, A163626. Sequence in context: A006741 A120573 A260345 * A259817 A230842 A000911 Adjacent sequences:  A028241 A028242 A028243 * A028245 A028246 A028247 KEYWORD nonn AUTHOR N. J. A. Sloane, Doug McKenzie (mckfam4(AT)aol.com) STATUS approved

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Last modified January 20 10:18 EST 2022. Contains 350471 sequences. (Running on oeis4.)