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A137925
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a(n) = the largest divisor of n that is coprime to A002808(n). (A002808(n) = the n-th composite.).
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2
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1, 1, 3, 4, 1, 1, 1, 8, 9, 5, 11, 4, 13, 7, 3, 1, 17, 9, 19, 5, 7, 11, 23, 1, 25, 2, 27, 1, 29, 2, 31, 1, 33, 17, 35, 9, 37, 38, 39, 40, 41, 7, 43, 44, 45, 46, 47, 3, 49, 1, 17, 13, 53, 27, 5, 7, 57, 58, 59, 5, 61, 31, 7, 1, 13, 66, 67, 68, 69, 14, 71, 9, 73, 37, 25, 19, 11, 39, 79, 1, 1
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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EXAMPLE
| The 12th composite is 21. The divisors of 12 are 1,2,3,4,6,12. The divisors of 12 that are coprime to 21 are 1,2,4. 4 is the largest of these; so a(12) = 4.
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MAPLE
| A002808 := proc(n) option remember ; local a; if n = 1 then 4; else for a from A002808(n-1)+1 do if not isprime(a) then RETURN(a) ; fi ; od: fi ; end: A137925 := proc(n) local dvs, d, a002808 ; a002808 := A002808(n) ; dvs := sort(convert(numtheory[divisors](n), list), `>`) ; for d in dvs do if gcd(d, a002808) = 1 then RETURN(d) ; fi ; od: end: seq(A137925(n), n=1..120) ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 17 2008
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CROSSREFS
| Cf. A137924.
Sequence in context: A176979 A058022 A139344 * A171528 A131107 A046547
Adjacent sequences: A137922 A137923 A137924 * A137926 A137927 A137928
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Feb 23 2008
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EXTENSIONS
| More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 17 2008
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