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A130802 a(1) = 1; a(n+1) = Sum_{k=1..n} (a(k)-th integer from among those positive integers which are coprime to (n+1-k)). 1
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, 100400469160 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..800

EXAMPLE

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.

MAPLE

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);  # Alois P. Heinz, Aug 05 2009

CROSSREFS

Cf. A132273, A132274, A132275.

Sequence in context: A001385 A039808 A138164 * A022543 A036618 A003018

Adjacent sequences:  A130799 A130800 A130801 * A130803 A130804 A130805

KEYWORD

nonn

AUTHOR

Leroy Quet, Aug 20 2007

EXTENSIONS

More terms from Alois P. Heinz, Aug 05 2009

STATUS

approved

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Last modified October 17 01:09 EDT 2018. Contains 316275 sequences. (Running on oeis4.)