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A155090
Composites k such that composite(k) is odd.
0
4, 8, 12, 15, 21, 26, 30, 33, 35, 38, 40, 44, 46, 49, 55, 58, 63, 66, 68, 70, 77, 81, 84, 86, 88, 90, 92, 94, 100, 102, 106, 108, 110, 112, 116, 118, 121, 123, 126, 129, 134, 136, 140, 142, 144, 146, 150, 154, 156, 158, 160, 162, 165, 169, 171, 176, 180, 183, 185
OFFSET
1,1
EXAMPLE
4 (composite) is a term because composite(4) = 9;
8 (composite) is a term because composite(8) = 15;
12 (composite) is a term because composite(12) = 21.
MAPLE
A002808 := proc(n) option remember ; 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:
isA002808 := proc(n) n >= 4 and not isprime(n) ; end proc:
for i from 1 to 400 do if isA002808(i) then c := A002808(i) ; if type(c, 'odd') then printf("%d, ", i) ; end if; end if; end do: # R. J. Mathar, May 10 2010
MATHEMATICA
seq[nmax_] := Module[{m, sq, cc}, For[m = nmax, True, m = m+nmax, sq = Select[cc = Select[Range[m], CompositeQ], If[# <= Length[cc], OddQ[cc[[#]]], False]&]; If[Length[sq] > nmax, Return[Take[sq, nmax]]]]];
seq[59] (* Jean-François Alcover, Jul 08 2022 *)
CROSSREFS
Cf. A002808.
Sequence in context: A311109 A311110 A311111 * A311112 A311113 A311114
KEYWORD
nonn
AUTHOR
EXTENSIONS
Entries checked by R. J. Mathar, May 10 2010
Name and Example section simplified by Jon E. Schoenfield, Feb 10 2019
STATUS
approved