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Search: id:A116204
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| A116204 |
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a(0) = 1; for n>=1, a(n) = the number of positive divisors of n which are coprime to a(n-1). |
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2
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| 1, 1, 2, 2, 1, 2, 2, 2, 1, 3, 4, 2, 2, 2, 2, 4, 1, 2, 3, 2, 2, 4, 2, 2, 2, 3, 4, 4, 2, 2, 4, 2, 1, 4, 2, 4, 3, 2, 2, 4, 2, 2, 4, 2, 2, 6, 2, 2, 2, 3, 6, 2, 2, 2, 4, 4, 2, 4, 2, 2, 4, 2, 2, 6, 1, 4, 4, 2, 2, 4, 4, 2, 3, 2, 2, 6, 2, 4, 4, 2, 2, 5, 4, 2, 4, 4, 2, 4, 2, 2, 6, 4, 2, 4, 2, 4, 2, 2, 3, 2, 3, 2, 4, 2, 2
(list; graph; listen)
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OFFSET
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0,3
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EXAMPLE
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a(11) = 2. There are 2 positive divisors (1 and 3) of 12 which are coprime to 2. So a(12) = 2.
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MAPLE
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with(numtheory): a[0]:=1: for n from 1 to 140 do ct:=0: div:=divisors(n): for j from 1 to tau(n) do if igcd(div[j], a[n-1])=1 then ct:=ct+1 else ct:=ct: fi: od: a[n]:=ct: od: seq(a[n], n=0..140); (Deutsch)
A116204 := proc(nmax) local a, n, dvs, resl, d ; a := [1] ; while nops(a) < nmax do n := nops(a) ; dvs := numtheory[divisors](n) ; resl :=0 ; for d from 1 to nops(dvs) do if gcd(op(d, dvs), op(-1, a)) = 1 then resl := resl+1 ; fi ; od ; a := [op(a), resl] ; od ; RETURN(a) ; end: A116204(100) ; (Mathar)
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CROSSREFS
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Sequence in context: A037196 A116543 A107260 this_sequence A106054 A023568 A081753
Adjacent sequences: A116201 A116202 A116203 this_sequence A116205 A116206 A116207
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet (qq-quet(AT)mindspring.com), Apr 16 2007
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl) and Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 27 2007
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