A079672 Numbers of the form (3^s+1)/(3^r+1) for s > 1, 1 <= r <= s-1.

7, 61, 73, 547, 4921, 703, 5905, 44287, 6481, 398581, 478297, 3587227, 512461, 58807, 32285041, 38742049, 530713, 290565367, 42521761, 2615088301, 373584043, 4780783, 3138105961, 23535794707, 43040161, 211822152361, 3472494301

Offset: 1

Author

Jose R. Brox (tautocrona(AT)terra.es), Jan 25 2003

Keywords

• nonn

Comments

(b^s+1) / (b^r+1) is an integer iff s/r is odd. - Jose Brox (tautocrona(AT)terra.es), Dec 27 2005

Crossrefs

Cf. A079665, A079581, A079673.

Programs

PARI

for(x=2,26, for(y=1,x-1,if(Mod(2^x+1,2^y+1),0,print1((3^x+1)/(3^y+1)",")))) \\ The Mod(2^x+1,2^y+1) is not a bug, since the exponents do not depend on the base in which they are calculated.