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A084127 Prime factor >= other prime factor of n-th semiprime. 43
2, 3, 3, 5, 7, 5, 7, 11, 5, 13, 11, 17, 7, 19, 13, 23, 7, 17, 11, 19, 29, 31, 13, 23, 37, 11, 41, 17, 43, 29, 13, 31, 47, 19, 53, 37, 23, 59, 17, 11, 61, 41, 43, 19, 67, 47, 71, 13, 29, 73, 31, 79, 53, 23, 83, 13, 59, 89, 61, 37, 17, 97, 67, 101, 29, 41, 103, 19, 71, 107, 43, 31 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Largest nontrivial divisor of n-th semiprime. [Juri-Stepan Gerasimov, Apr 18 2010]
Greater of the prime factors of A001358(n). - Jianing Song, Aug 05 2022
LINKS
Eric Weisstein's World of Mathematics, Semiprime
FORMULA
a(n) = A006530(A001358(n)).
a(n) = A001358(n)/A020639(A001358(n)). [corrected by Michel Marcus, Jul 18 2020]
a(n) = A001358(n)/A084126(n).
MATHEMATICA
FactorInteger[#][[-1, 1]]& /@ Select[Range[1000], PrimeOmega[#] == 2&] (* Jean-François Alcover, Nov 17 2021 *)
PROG
(Haskell)
a084127 = a006530 . a001358 -- Reinhard Zumkeller, Nov 25 2012
(PARI) lista(nn) = {for (n=2, nn, if (bigomega(n)==2, f = factor(n); print1(f[length(f~), 1], ", ")); ); } \\ Michel Marcus, Jun 05 2013
CROSSREFS
Cf. A001358 (the semiprimes), A084126 (lesser of the prime factors of the semiprimes).
Sequence in context: A066072 A239586 A180611 * A089934 A113460 A113470
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 15 2003
EXTENSIONS
Corrected by T. D. Noe, Nov 15 2006
STATUS
approved

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Last modified February 26 13:41 EST 2024. Contains 370352 sequences. (Running on oeis4.)