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Search: id:A130802
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| A130802 |
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a(1)=1. a(n+1) = sum{k=1 to n} (a(k)th integer from among those positive integers which are coprime to (n+1-k)). |
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1
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| 1, 1, 2, 4, 9, 20, 47, 110, 260, 614, 1448, 3421, 8081, 19092, 45107, 106567, 251768, 594816, 1405285, 3320066, 7843851, 18531547, 43781846, 103437135, 244376187, 577352823, 1364029309, 3222597827, 7613573030, 17987504932, 42496516727
(list; graph; listen)
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OFFSET
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1,3
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LINKS
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Leroy Quet, Home Page (listed in lieu of email address)
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EXAMPLE
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The integers coprime to 5 are 1,2,3,4,6,.. The a(1)th=1st of these is 1. The integers coprime to 4 are 1,3,5,.. The a(2)th=1st of these is 1. The integers coprime to 3 are 1,2,4,5,.. The a(3)th=2nd of these is 2. The integers coprime to 2 are 1,3,5,7,9,.. The a(4)th=4th of these is 7. And the integers coprime to 1 are 1,2,3,4,5,6,7,8,9,10,.. The a(5)th=9th of these is 9. So a(6) = 1 + 1 + 2 + 7 + 9 = 20.
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MAPLE
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with (numtheory): fc:= proc(t, p) option remember; local m, j, h, pp; if p=1 then t else pp:= phi(p); m:= iquo(t, pp); j:= m*pp; h:= m*p-1; while j<t do h:= h+1; if igcd(p, h)=1 then j:= j+1 fi od; h fi end: a:= proc(n) option remember; `if` (n=1, 1, add (fc(a(k), (n-k)), k=1..n-1)) end: seq (a(n), n=1..35); [From Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 05 2009]
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CROSSREFS
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Cf. A132273, A132274, A132275.
Sequence in context: A001385 A039808 A138164 this_sequence A022543 A036618 A003018
Adjacent sequences: A130799 A130800 A130801 this_sequence A130803 A130804 A130805
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet Aug 20 2007
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EXTENSIONS
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a(10) - a(31) from Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 05 2009
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