A175104 a(1)=1. For n >= 2, a(n) = 2*a(n-1) + (number of composites among first n-1 terms of the sequence).

1, 2, 4, 9, 20, 43, 89, 181, 365, 734, 1473, 2952, 5911, 11830, 23669, 47347, 94704, 189419, 378850, 757713, 1515440, 3030895, 6061806, 12123629, 24247276, 48494571, 96989162, 193978345, 387956712, 775913447, 1551826917, 3103653858

Offset

1,2

Links

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

Maple

A175104 := proc(n) option remember; if n = 1 then 1; else a := 2*procname(n-1) ; for i from 1 to n-1 do prev := procname(i) ; if prev > 2 and not isprime(prev) then a := a+1 ; end if; end do ; a ; end if; end proc: seq(A175104(n), n=1..70) ; # R. J. Mathar, Feb 16 2010

Mathematica

nxt[{a_, c_}]:=Module[{t=2a+c}, {t, c+If[CompositeQ[t], 1, 0]}]; Transpose[ NestList[ nxt, {1, 0}, 40]][[1]] (* Harvey P. Dale, Mar 07 2015 *)

Crossrefs

Sequence in context: A018102 A018103 A350092 * A123720 A179744 A266930

Adjacent sequences: A175101 A175102 A175103 * A175105 A175106 A175107

Keyword

nonn

Author

Leroy Quet, Feb 09 2010

Extensions

More terms from R. J. Mathar, Feb 16 2010

Status

approved