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Search: id:A161990
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| A161990 |
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Composites which have the same largest prime factor as their index. |
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1
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| 10, 12, 14, 25, 36, 39, 42, 45, 77, 124, 132, 140, 147, 224, 234, 266, 345, 365, 370, 375, 380, 385, 390, 494, 621, 638, 660, 671, 682, 782, 899, 945, 1001, 1086, 1140, 1377, 1558, 1577, 1628, 1696, 1728, 1760, 1798, 1885, 2046, 2145, 2484, 2550, 2970, 3101, 3122, 3477
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If A052369(k) = A006530(k), we add the associated composite A002808(k) to the sequence.
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EXAMPLE
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The 6th composite is 12=2^2*3 with largest prime factor 3, and the largest
prime factor of the index 6=2*3 is also 3, which adds 12 to the sequence.
The 7th composite is 14=2*7 with largest prime factor 7, and the largest
prime factor of the index 7 is also 7, which adds 14 to the sequence.
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MAPLE
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A006530 := proc(n) sort(convert(numtheory[factorset](n), list)); op(-1, %) ; end:
A002808 := proc(n) if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end:
A052369 := proc(n) A006530(A002808(n)) ; end:
for n from 1 to 10000 do if A052369(n) = A006530(n) then printf("%d, ", A002808(n)) ; fi; od: # R. J. Mathar, Aug 14 2009
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CROSSREFS
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Cf. A002808, A050696.
Sequence in context: A116612 A068502 A109959 this_sequence A030591 A006793 A054518
Adjacent sequences: A161987 A161988 A161989 this_sequence A161991 A161992 A161993
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Jun 24 2009
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EXTENSIONS
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Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 14 2009
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