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 A154370 Numbers k such that gpf(composite(k)) - lpf(composite(k)) is prime. 2
 5, 7, 8, 11, 16, 18, 19, 23, 25, 27, 28, 30, 34, 36, 39, 42, 43, 50, 53, 54, 56, 57, 60, 62, 65, 72, 74, 76, 82, 83, 89, 91, 93, 95, 98, 102, 105, 108, 111, 114, 115, 119, 122, 128, 132, 134, 138, 139, 143, 147, 151, 153, 159, 161, 163, 170, 175, 176, 178, 182, 187 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE Composite(5) = 10 = 5*2 and 5 - 2 = 3 (prime), so 5 is a term; composite(7) = 14 = 7*2 and 7 - 2 = 5 (prime), so 7 is a term; composite(8) = 15 = 5*3 and 5 - 3 = 2 (prime), so 8 is a term; composite(11) = 20 = 5*2*2 and 5 - 2 = 3 (prime), so 11 is a term. MAPLE A020639 := proc(n) numtheory[factorset](n) ; min(op(%)) ; end proc: A006530 := proc(n) numtheory[factorset](n) ; max(op(%)) ; end proc: for n from 1 to 500 do if isprime( A006530(A002808(n)) - A020639(A002808(n)) ) then printf("%d, ", n ) ; end if; end do: # R. J. Mathar, May 05 2010 MATHEMATICA Flatten @ Position[Select[Range[1000], CompositeQ], c_Integer /; PrimeQ[Last[#] - First[#]& @ FactorInteger[c][[All, 1]]]] (* Jean-François Alcover, Jul 24 2020 *) CROSSREFS Cf. A000040 (primes), A002808 (composites). Cf. A006530 (gpf), A020639 (lpf). Sequence in context: A191929 A082728 A285081 * A045251 A099497 A327960 Adjacent sequences:  A154367 A154368 A154369 * A154371 A154372 A154373 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Jan 08 2009 EXTENSIONS Corrected (30 inserted, 43 inserted, 100 removed, ...) by R. J. Mathar, May 05 2010 STATUS approved

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Last modified July 28 10:51 EDT 2021. Contains 346326 sequences. (Running on oeis4.)