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Search: id:A132275
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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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+0
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
(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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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 .
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MAPLE
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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]
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CROSSREFS
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Cf. A132273, A132274.
Sequence in context: A076892 A106462 A129987 this_sequence A136671 A024557 A025241
Adjacent sequences: A132272 A132273 A132274 this_sequence A132276 A132277 A132278
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KEYWORD
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nonn
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AUTHOR
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Leroy Quet Aug 16 2007
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EXTENSIONS
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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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