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Search: id:A134382
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| A134382 |
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a(n) is the smallest number k larger than a(n-1) such that n*nd(k)*sopf(k)=sigma(k), where nd is the number of divisors (A000005) and sopf the sum of prime factors without repetition (A008472). |
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+0
5
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| 20, 140, 464, 660, 1276, 1365, 2204, 2508, 2805, 2907, 5590, 5698, 5742, 6006, 7395, 8680, 14645, 15052, 18875, 19170, 19740, 23871, 34579, 34804, 35164, 35244, 35934, 38121, 106805, 114953, 261536
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Sequence suggested by Puzzle 419 in Carlos Rivera's The Prime Puzzles & Problems Connection
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FORMULA
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a(n)>a(n-1): n*A000005(a(n))*A001221(a(n))=A000203(a(n)) . - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 16 2007
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MAPLE
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A001221 := proc(n) local divs, i ; if n = 1 then 0; else divs := ifactors(n)[2] ; add( op(1, i), i=divs) ; fi ; end: A134382 := proc(n) option remember ; local k, kmin ; if n = 1 then kmin := 1 ; else kmin := A134382(n-1)+1 ; fi ; for k from kmin do if numtheory[sigma](k) = n* numtheory[tau](k)*A001221(k) then RETURN(k) ; fi ; od: end: for n from 1 to 30 do print( A134382(n)) ; od: - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 16 2007
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CROSSREFS
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Cf. A134383 A134384 A134385 A134386.
Sequence in context: A105573 A144965 A140301 this_sequence A105939 A054389 A071816
Adjacent sequences: A134379 A134380 A134381 this_sequence A134383 A134384 A134385
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KEYWORD
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easy,more,nonn
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AUTHOR
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Enoch Haga (Enokh(AT)comcast.net), Oct 23 2007
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EXTENSIONS
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Edited by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 16 2007
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