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A072261 a(n) = 4*a(n-1)+1, a(1)=7. 4
7, 29, 117, 469, 1877, 7509, 30037, 120149, 480597, 1922389, 7689557, 30758229, 123032917, 492131669, 1968526677, 7874106709, 31496426837, 125985707349, 503942829397, 2015771317589, 8063085270357, 32252341081429 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These are the integers N which on application of the Collatz function yield the number 11. 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 11).

These numbers reach 11 in Collatz function iteration after 2(n+1) steps and so end in 1 after exactly 2n+18 steps. - Lambert Klasen (lambert.klasen(AT)gmx.de), Nov 08 2004

Numbers whose binary representation is 111 together with n - 1 times 01. For example, a(4) = 469 = 111010101 (2). - Omar E. Pol, Nov 24 2012

LINKS

Table of n, a(n) for n=1..22.

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

FORMULA

a(n) = (11*4^n-2)/6 = 22*A002450(n-1)+7. - Lambert Klasen (lambert.klasen(AT)gmx.de), Nov 08 2004

MATHEMATICA

a[n_] := 4a[n - 1] + 1; a[1] = 7; Table[ a[n], {n, 1, 25}]

CROSSREFS

Cf. A072257-A072260, A072262, A099730.

Sequence in context: A296646 A037094 A118171 * A066744 A037576 A327587

Adjacent sequences:  A072258 A072259 A072260 * A072262 A072263 A072264

KEYWORD

nonn,easy

AUTHOR

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

EXTENSIONS

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

STATUS

approved

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Last modified September 21 00:17 EDT 2019. Contains 327252 sequences. (Running on oeis4.)