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 A188716 a(n) = n + (n-1)*(2^n-2). 3
 1, 1, 4, 15, 46, 125, 316, 763, 1786, 4089, 9208, 20471, 45046, 98293, 212980, 458739, 983026, 2097137, 4456432, 9437167, 19922926, 41943021, 88080364, 184549355, 385875946, 805306345, 1677721576, 3489660903, 7247757286, 15032385509, 31138512868, 64424509411, 133143986146, 274877906913, 566935683040, 1168231104479 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Number of elements in the semi-group IDT_n. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 Index entries for linear recurrences with constant coefficients, signature (6,-13,12,-4). FORMULA a(n) = 6*a(n-1)-13*a(n-2)+12*a(n-3)-4*a(n-4). G.f.: (1-5*x+11*x^2-8*x^3)/((1-x)^2*(1-2*x)^2). [Colin Barker, Apr 06 2012] a(n) = A000337(n) - (n-1). - Andrew Penland , Mar 24 2016 PROG (MAGMA) [n + (n-1)*(2^n-2): n in [0..50]]; // Vincenzo Librandi, May 01 2011 (PARI) a(n)=(n-1)<

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Last modified May 11 10:09 EDT 2021. Contains 343788 sequences. (Running on oeis4.)