1,1

These are the integers N which on application of the Collatz function yield the number 17. The Collatz function: if N is an odd number then (3N+1)/2^r yields a positive odd integer for some value of r (which in this case is 17).

Numbers whose binary representation is 1011 together with n - 1 times 01. For example, a(4) = 725 = 1011010101 (2). - Omar E. Pol, Nov 24 2012

G. C. Greubel, Table of n, a(n) for n = 1..1000

Index entries for linear recurrences with constant coefficients, signature (5,-4).

From Bruno Berselli, Dec 16 2011: (Start)

G.f.: x*(11-10*x)/(1-5*x+4*x^2).

a(n) = (17*2^(2*n-1) - 1)/3.

Sum_{i=1..n} a(i) = (a(n+1) - n + 1)/3 - 4. (End)

a(n) = 34*A002450(n-1) + 11 . - Yosu Yurramendi, Jan 24 2017

E.g.f.: (-15 - 2*exp(x) + 17*exp(4*x))/6. - G. C. Greubel, Jan 14 2020

a(n) = A178415(6, n) = A347834(5, n-1), arrays, for n >= 1. - Wolfdieter Lang, Nov 29 2021

seq( (17*4^n -2)/6, n=1..30); # G. C. Greubel, Jan 14 2020

a[n_]:= 4a[n-1] +1; a[1]=11; Table[a[n], {n, 25}]

NestList[4#+1&, 11, 30] (* or *) LinearRecurrence[{5, -4}, {11, 45}, 30] (* Harvey P. Dale, Dec 25 2014 *)

(PARI) vector(30, n, (17*4^n -2)/6) \\ G. C. Greubel, Jan 14 2020

(Magma) [(17*4^n -2)/6: n in [1..30]]; // G. C. Greubel, Jan 14 2020

(SageMath) [(17*4^n -2)/6 for n in (1..30)] # G. C. Greubel, Jan 14 2020

(GAP) List([1..30], n-> (17*4^n -2)/6); # G. C. Greubel, Jan 14 2020

Cf. A072257, A072258, A072259, A072260, A072261, A099730, A178415, A347834.

Sequence in context: A370534 A263227 A144932 * A231224 A231438 A322560

Adjacent sequences: A072259 A072260 A072261 * A072263 A072264 A072265

nonn,easy

N. Rathankar (rathankar(AT)yahoo.com), Jul 08 2002

Edited and extended by Robert G. Wilson v, Jul 17 2002

approved