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 A121367 a(1) = a(2) = 1, a(n) = a(n-1) + A007947(a(n-2)) for n >= 3, i.e., a(n) = a(n-1) plus the largest squarefree divisor of a(n-2). 2
 1, 1, 2, 3, 5, 8, 13, 15, 28, 43, 57, 100, 157, 167, 324, 491, 497, 988, 1485, 1979, 2144, 4123, 4257, 8380, 9799, 13989, 23788, 37777, 49671, 87448, 104005, 125867, 229872, 355739, 384473, 740212, 1124685, 1494791, 1536446, 3031237, 4567683, 7598920 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS EXAMPLE 14 is the largest squarefree divisor of a(9) = 28. So a(11) = a(10) + 14 = 57. MAPLE with(numtheory): A007947 := proc(n) local i, t1, t2; t1 := ifactors(n)[2]; t2 := mul(t1[i][1], i=1..nops(t1)); end: a:=proc(n) if n=1 or n=2 then 1 else a(n-1)+A007947(a(n-2)) fi end: seq(a(n), n=1..20); # Emeric Deutsch, Jul 24 2006 MATHEMATICA nxt[{a_, b_}]:={b, b+Max[Select[Divisors[a], SquareFreeQ]]}; Transpose[ NestList[ nxt, {1, 1}, 50]][[1]] (* Harvey P. Dale, Jul 23 2015 *) CROSSREFS Cf. A007947, A121368, A121369. Sequence in context: A138183 A076591 A078695 * A308495 A221672 A241551 Adjacent sequences:  A121364 A121365 A121366 * A121368 A121369 A121370 KEYWORD nonn AUTHOR Leroy Quet, Jul 23 2006 EXTENSIONS More terms from Emeric Deutsch, Jul 24 2006 More terms from R. J. Mathar, May 11 2007 STATUS approved

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Last modified May 17 22:15 EDT 2021. Contains 343992 sequences. (Running on oeis4.)