A079665 - OEIS

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

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OFFSET

1,1

COMMENTS

Conjecture: (b^s+1)/(b^r+1) is an integer if and only if: 1) r<s/2, 2) if s==1 (mod 2) then r is divisor of s, 3) if s=k*2^t with gcd(k,2^t)=1 then r is 2^t*u with u dividing k

LINKS

Table of n, a(n) for n=1..34.

EXAMPLE

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

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