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A165897
a(n) = a(n-1) + largest proper divisor of a(n-1), a(1)=4.
1
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
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
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, Sep 29 2009
STATUS
approved