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A154373 Composites k such that gpf(k) - lpf(k) is an odd nonprime. 1
6, 12, 18, 22, 24, 34, 36, 44, 46, 48, 54, 58, 66, 68, 72, 74, 82, 88, 92, 94, 96, 102, 106, 108, 110, 116, 118, 132, 134, 136, 138, 142, 144, 148, 154, 158, 162, 164, 166, 170, 174, 176, 178, 184, 188, 192, 194, 198, 202, 204, 212, 214, 216, 220, 222, 226, 230 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

6 = 3*2 and 3 - 2 = 1 (odd nonprime), so 6 is a term;

12 = 3*2*2 and 3 - 2 = 1 (odd nonprime), so 12 is a term;

18 = 3*3*2 and 3 - 2 = 1 (odd nonprime), so 18 is a term;

22 = 11*2 and 11 - 2 = 9 (odd nonprime), so 22 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 c := A006530(A002808(n)) - A020639(A002808(n)) ; if type(c, 'odd') and not isprime(c) then printf("%d, ", A002808(n) ) ; end if; end do: # R. J. Mathar, May 05 2010

MATHEMATICA

lpfQ[n_]:=Module[{fi=Transpose[FactorInteger[n]][[1]], c}, c= Last[fi]-First[fi]; OddQ[c]&&!PrimeQ[c]]; Select[Range[300], lpfQ] (* Harvey P. Dale, Nov 25 2012 *)

CROSSREFS

Cf. A002808 (composites), A141468 (odd nonprimes).

Cf. A006530 (gpf), A020639 (lpf).

Sequence in context: A160594 A315724 A146538 * A315725 A315726 A315727

Adjacent sequences:  A154370 A154371 A154372 * A154374 A154375 A154376

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jan 08 2009

EXTENSIONS

Corrected (69 replaced by 68, 203 removed) by R. J. Mathar, May 05 2010

STATUS

approved

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Last modified November 14 02:19 EST 2019. Contains 329108 sequences. (Running on oeis4.)