A154373 Composites k such that gpf(k) - lpf(k) is an odd nonprime.

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

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