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 A006528 a(n) = (n^4 + n^2 + 2*n)/4. (Formerly M4160) 12
 0, 1, 6, 24, 70, 165, 336, 616, 1044, 1665, 2530, 3696, 5226, 7189, 9660, 12720, 16456, 20961, 26334, 32680, 40110, 48741, 58696, 70104, 83100, 97825, 114426, 133056, 153874, 177045, 202740, 231136, 262416, 296769, 334390, 375480 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Number of ways to color vertices of a square using <= n colors, allowing only rotations. Also product of first and last terms in n-th row of a triangle of form: row(1)= 1; row(2)= 2,3; row(3)= 4,5,6,.... - Dave Durgin, Aug 17 2012 REFERENCES Nick Baxter, The Burnside di-lemma: combinatorics and puzzle symmetry, in Tribute to a Mathemagician, Peters, 2005, pp. 199-210. M. Gardner, New Mathematical Diversions from Scientific American. Simon and Schuster, NY, 1966, p. 246. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992. Simon Plouffe, 1031 Generating Functions and Conjectures, Université du Québec à Montréal, 1992. Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = n*(n+1)*(n^2-n+2)/4. a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5). [Vincenzo Librandi, Apr 30 2012] MAPLE A006528:=-z*(1+z+4*z**2)/(z-1)**5; # Simon Plouffe in his 1992 dissertation a:=n->add(n+add(binomial(n, 2), j=1..n), j=0..n):seq(a(n)/2, n=0..35); # Zerinvary Lajos, Aug 26 2008 MATHEMATICA Table[CycleIndex[CyclicGroup[4], t]/.Table[t[i]->n, {i, 1, 4}], {n, 0, 20}] (* Geoffrey Critzer, Mar 13 2011*) Table[(n^4+n^2+2*n)/4, {n, 0, 40}] (* or *) LinearRecurrence[{5, -10, 10, -5, 1}, {0, 1, 6, 24, 70}, 40] (* Harvey P. Dale, Jan 13 2019 *) PROG (MAGMA) I:=[0, 1, 6, 24, 70]; [n le 5 select I[n] else 5*Self(n-1)-10*Self(n-2)+10*Self(n-3)-5*Self(n-4)+Self(n-5): n in [1..40]]; // Vincenzo Librandi, Apr 30 2012 (PARI) a(n) = n*(n+1)*(n^2-n+2)/4; /* Joerg Arndt, Apr 30 2012 */ CROSSREFS Cf. A002817 (square colorings). Sequence in context: A092348 A274772 A234271 * A052749 A262445 A090574 Adjacent sequences:  A006525 A006526 A006527 * A006529 A006530 A006531 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified October 14 07:31 EDT 2019. Contains 327995 sequences. (Running on oeis4.)