A079665 Triangular array read by rows: row s contains integers of the form (2^s+1)/(2^r+1) in order of increasing r <= s-1.

3, 11, 13, 43, 171, 57, 205, 683, 241, 2731, 3277, 10923, 3641, 993, 43691, 52429, 4033, 174763, 61681, 699051, 233017, 16257, 838861, 2796203, 65281, 11184811, 1016801, 13421773, 44739243, 14913081, 261633, 15790321, 178956971, 214748365

Offset: 1

Author

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

Keywords

• nonn
• tabf

Comments

Conjecture: (b^s+1)/(b^r+1) is an integer if and only if: 1) r

Examples

			s=2: no terms
s=3: 3
s=4: no terms
s=5: 11
s=6: 13
s=7: 43
s=8: no terms
s=9: 171, 57
...
		

Crossrefs

Cf. A079672, A079581, A079673, A370425.

Programs

PARI

for(x=2,30, for(y=1,x-1,if(Mod(2^x+1,2^y+1),0,print1((2^x+1)\(2^y+1)","))))

Extensions

Definition corrected by Max Alekseyev, Feb 18 2024

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