A165897 a(n) = a(n-1) + largest proper divisor of a(n-1), a(1)=4.

4, 6, 9, 12, 18, 27, 36, 54, 81, 108, 162, 243, 324, 486, 729, 972, 1458, 2187, 2916, 4374, 6561, 8748, 13122, 19683, 26244, 39366, 59049, 78732, 118098, 177147, 236196, 354294, 531441, 708588, 1062882, 1594323, 2125764, 3188646, 4782969

Offset

1,1

Links

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

Index entries for linear recurrences with constant coefficients, signature (0,0,3).

Formula

a(1)=4, a(2)=6, a(3)=9, a(n) = 3*a(n-3) for n>3.

G.f.: x*(4+6*x+9*x^2) / ( 1-3*x^3 ). - R. J. Mathar, Nov 07 2015

Mathematica

NestList[ #+Divisors[ # ][[ -2]]&, 4, 50]
LinearRecurrence[{0, 0, 3}, {4, 6, 9}, 50] (* G. C. Greubel, Apr 17 2016 *)

Crossrefs

Cf. A000792.

Sequence in context: A088765 A175250 A078782 * A020165 A368196 A110607

Adjacent sequences: A165894 A165895 A165896 * A165898 A165899 A165900

Keyword

nonn,easy

Author

Zak Seidov, Sep 29 2009

Status

approved