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A132275 a(1)=1. a(n+1) = sum{k=1 to n} (a(k)th integer from among those positive integers which are coprime to a(n+1-k)). +0
4
1, 1, 2, 4, 8, 17, 37, 81, 177, 387, 847, 1856, 4066, 8910, 19524, 42783, 93760, 205475, 450282, 986770, 2162473, 4738974, 10385267, 22758885, 49875175, 109299427, 239525260, 524909877, 1150318695, 2520876742, 5524399079, 12106496388 (list; graph; listen)
OFFSET

1,3

LINKS

Leroy Quet, Home Page (listed in lieu of email address)

EXAMPLE

To compute a(5) we add the 1st integer coprime to a(4), the 1st integer coprime to a(3), the 2nd integer coprime to a(2) and the 4th integer coprime to a(1),

which is the 1st integer in {1,3,4,5,..}, the 1st integer in {1,2,3,4,...}, the 2nd integer in {1,2,3,4,...} and the 4th integer in {1,2,3,4,..}

= 1+1+2+4=8 .

MAPLE

A132275 := proc(n) option remember; local a, k, an1k, kcoud, c ; if n = 1 then 1; else a :=0 ; for k from 1 to n-1 do an1k := procname(n-k) ; kcoud := 0 ; for c from 1 do if gcd(c, an1k) = 1 then kcoud := kcoud+1 ; fi; if kcoud = procname(k) then a := a+c ; break; fi; od: od: a; fi; end:

seq(A132275(n), n=1..18) ; # R. J. Mathar, Jul 20 2009

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), a(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]

CROSSREFS

Cf. A132273, A132274.

Sequence in context: A076892 A106462 A129987 this_sequence A136671 A024557 A025241

Adjacent sequences: A132272 A132273 A132274 this_sequence A132276 A132277 A132278

KEYWORD

nonn

AUTHOR

Leroy Quet Aug 16 2007

EXTENSIONS

Corrected from a(5) on by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 21 2009

a(19) - a(32) from Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 05 2009

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.


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