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Search: id:A130157
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| A130157 |
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a(1)=1. a(n) = number of earlier terms of {a(k)} which are coprime to A130158(n-1), where sequence A130158 is a concatenation of the positive divisors of the terms of {a(k)}. |
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+0
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| 1, 1, 2, 3, 3, 5, 4, 7, 6, 9, 9, 11, 9, 10, 14, 13, 16, 11, 12, 7, 20, 14, 15, 23, 16, 17, 26, 25, 28, 21, 21, 31, 20, 27, 18, 35, 22, 29, 18, 39, 37, 41, 26, 26, 26, 26, 46, 44, 48, 26, 35, 27, 17, 18, 54, 46, 56, 29, 30, 50, 25, 25, 62, 32, 54, 26, 66, 46, 56, 38, 70, 67, 72, 33
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OFFSET
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1,3
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EXAMPLE
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{a(k)} begins: 1,1,2,3,3,5,4,... So sequence A130158 begins: 1,1,1,2,1,3,1,3,1,5,1,2,4,... So for example, a(7) is the number of terms from among (1,1,2,3,3,5) which are coprime to A130158(6) = 3. Therefore a(7) = 4.
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MAPLE
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A130157 := proc(nmax) local a, a130158, n, anext, i ; a := [1] ; a130158 := [] ; while nops(a) < nmax do n := nops(a)+1 ; a130158 := [op(a130158), op(numtheory[divisors](op(-1, a)))] ; anext :=0 ; for i from 1 to nops(a) do if gcd(op(i, a), op(n-1, a130158)) = 1 then anext := anext+1 ; fi ; od ; a := [op(a), anext] ; od ; RETURN(a) ; end: A130157(80) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 12 2007
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CROSSREFS
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Cf. A130158.
Adjacent sequences: A130154 A130155 A130156 this_sequence A130158 A130159 A130160
Sequence in context: A057859 A029579 A106647 this_sequence A103310 A046146 A081768
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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), May 13 2007
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 12 2007
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