A215782 Odd tribonacci non-divisors.

27, 81, 91, 103, 135, 163, 189, 199, 203, 221, 243, 247, 273, 297, 305, 309, 351, 371, 377, 397, 405, 421, 455, 459, 489, 513, 515, 551, 559, 567, 597, 609, 621, 637, 663, 675, 721, 729, 741, 757, 779, 783, 815, 819, 837, 883, 891, 915, 927, 945, 991, 995, 999

Offset: 1

Author

V. Raman, Aug 23 2012

Keywords

• nonn

Comments

Odd numbers that do not divide any term of A000213. - N. J. A. Sloane, Aug 23 2012

There are several sequences that have the name "tribonacci". Sequence A000073 is another, but that one has terms divisible by any number. - T. D. Noe, Aug 28 2012

Links

• T. D. Noe, Table of n, a(n) for n = 1..1000
• Project Euler, Problem #225: Tribonacci non-divisors

Crossrefs

Cf. A000213, A046735.

Programs

Mathematica

t = {}; Do[a = {1, 1, 1}; a0 = a; done = False; While[s = Total[a]; a = RotateLeft[a]; a[[-1]] = Mod[s, n]; If[a[[-1]] == 0, done = True]; a != a0 && ! done]; If[! done, AppendTo[t, n]], {n, 1, 1087, 2}]; t (* T. D. Noe, Aug 28 2012 *)

PARI

is(n)=if(n%2==0 || n<9, return(0)); my(a=1,b=1,c=3,t=4); while(c!=1 || b!=1 || a!=1, [a,b,c]=[b,c,(a+b+c)%n]; if(c==0, return(0))); 1 \\ Charles R Greathouse IV, Jan 12 2017