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A132275
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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 a(n+1-k)).
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4
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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, 26530895539, 58141380910
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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EXAMPLE
| To compute a(5) we add the first integer coprime to a(4), the first integer coprime to a(3), the 2nd integer coprime to a(2) and the 4th integer coprime to a(1),
which is the first integer in {1,3,4,5,..}, the first 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 .
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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); # Alois P. Heinz, Aug 05 2009
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CROSSREFS
| Cf. A132273, A132274.
Sequence in context: A076892 A106462 A129987 * A136671 A024557 A199409
Adjacent sequences: A132272 A132273 A132274 * A132276 A132277 A132278
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Aug 16 2007
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EXTENSIONS
| Corrected from a(5) on by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 21 2009
Extended beyond a(19) Alois P. Heinz (heinz(AT)hs-heilbronn.de), Aug 05 2009
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