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 A028401 The (2^n+1)-th triangular number (cf. A000217). 6
 3, 6, 15, 45, 153, 561, 2145, 8385, 33153, 131841, 525825, 2100225, 8394753, 33566721, 134242305, 536920065, 2147581953, 8590131201, 34360131585, 137439739905, 549757386753, 2199026401281, 8796099313665, 35184384671745 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS Number of types of Boolean functions of n variables under a certain group. Also the number of ordered decompositions of 2^n into 3 nonnegative integers (e.g. 2=0+0+2=0+2+0=2+0+0=1+1+0=1+0+1=0+1+1). - Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Aug 02 2007 LINKS Vincenzo Librandi, Table of n, a(n) for n = 2..1000 Daniel Poveda Parrilla, Illustration of initial terms I. Strazdins, Universal affine classification of Boolean functions, Acta Applic. Math. 46 (1997), 147-167. Index entries for linear recurrences with constant coefficients, signature (7,-14,8). FORMULA a(n) = (3/8)*2^n + (1/32)*4^n + 1. a(n) = 3*A007581(n-2) = 3/4*A060919(n-1). - Ralf Stephan, Aug 23 2003 a(n) = (2^n+4)*(2^n+8)/32. - Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Aug 02 2007 G.f.: 3*x^2*(1-5*x+5*x^2)/((1-x)*(1-2*x)*(1-4*x)). - Colin Barker, Mar 09 2012 a(n) = a(n-1) + 3*A000217(2^(n-3)) for n > 2. - Daniel Poveda Parrilla, Dec 27 2016 CROSSREFS Equals 2 * A036562(n-4) - 1, n>3. Cf. A000217. Sequence in context: A067771 A289678 A056382 * A005655 A277063 A051169 Adjacent sequences:  A028398 A028399 A028400 * A028402 A028403 A028404 KEYWORD nonn,easy AUTHOR EXTENSIONS More terms from Vladeta Jovovic, Feb 24 2000 Simpler definition from Tamas Kalmar-Nagy (integers(AT)kalmarnagy.com), Aug 02 2007 STATUS approved

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Last modified February 18 00:19 EST 2019. Contains 320237 sequences. (Running on oeis4.)