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 A001344 a(n) = sum_{k=0..2} (n+k)! * C(2,k). (Formerly M1405 N0548) 4
 2, 5, 11, 38, 174, 984, 6600, 51120, 448560, 4394880, 47537280, 562464000, 7224940800, 100111334400, 1488257971200, 23625316915200, 398840682240000, 7134671351808000, 134805535248384000, 2682594582700032000, 56078391288471552000, 1228615514129203200000 (list; graph; refs; listen; history; text; internal format)
 OFFSET -1,1 COMMENTS If we discard the first two terms and set a(0)= 11 then a(n) = (n+1)!*(n^2+7*n+11). - Gary Detlefs, Aug 11 2010 For nonnegative n, a(n) equals the permanent of the (n+2) X (n+2) matrix with a 2 in the upper right corner, a 2 in the lower left corner, and 1's everywhere else. - John M. Campbell, May 25 2011 In factorial base representation (A007623) the terms of this sequence look as: 10, 21, 121, 1210, 12100, 121000, ... From a(1)=11 onward each term begins always with "121", which is then followed by n-1 zeros. - Antti Karttunen, Sep 23 2016 REFERENCES 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 T. D. Noe, Table of n, a(n) for n = -1..100 E. Biondi, L. Divieti, G. Guardabassi, Counting paths, circuits, chains and cycles in graphs: A unified approach, Canad. J. Math. 22 1970 22-35. FORMULA a(-1) = 2, for n >= 0, a(n) = A028387(1+n) * n! - Antti Karttunen, Sep 23 2016 MATHEMATICA Join[{2}, Table[Sum[(n + k)! Binomial[2, k], {k, 0, 2}], {n, 0, 20}]] (* T. D. Noe, Jun 28 2012 *) PROG (Scheme) (define (A001344 n) (cond ((= -1 n) 2) (else (* (A028387 (+ 1 n)) (A000142 n))))) ;; Antti Karttunen, Sep 23 2016 CROSSREFS Cf. A000142, A007623, A028387. From a(1) = 11 onward row 2 of A276588, row 8 of A276955. Sequence in context: A131581 A195985 A056301 * A056302 A276547 A065850 Adjacent sequences:  A001341 A001342 A001343 * A001345 A001346 A001347 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified April 7 19:16 EDT 2020. Contains 333306 sequences. (Running on oeis4.)