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A155109
Odd nonprime numbers k such that composite(k) is even.
0
1, 9, 25, 27, 39, 45, 51, 57, 65, 69, 75, 85, 87, 91, 93, 95, 99, 105, 111, 115, 117, 119, 125, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 175, 177, 187, 201, 207, 209, 213, 215, 217, 221, 231, 235, 237, 243, 247, 253, 255, 259, 261, 273, 275, 279, 287
OFFSET
1,2
MAPLE
isA002808 := proc(n) n >= 4 and not isprime(n) ; end proc:
A002808 := proc(n) option remember ; local a; if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do; end if; end proc:
for n from 1 to 400 do if type(n, 'odd') and not isprime(n) then c := A002808(n) ; if type(c, 'even') then printf("%d, ", n) ; end if; end if; end do: # R. J. Mathar, May 10 2010
MATHEMATICA
With[{nn=400}, Select[Flatten[Position[Complement[Range[4, nn], Prime[ Range[PrimePi[nn]]]], _?(EvenQ[#]&)]], OddQ[#]&&!PrimeQ[#]&]] (* Harvey P. Dale, Jun 23 2013 *)
CROSSREFS
Sequence in context: A304035 A339726 A377702 * A268576 A053850 A225498
KEYWORD
nonn,less
AUTHOR
EXTENSIONS
Edited by N. J. A. Sloane, Jan 30 2009
Corrected (67, 79, 113, 189, 219 removed) by R. J. Mathar, May 10 2010
STATUS
approved