OFFSET
1,1
COMMENTS
LINKS
Robert Israel, Table of n, a(n) for n = 1..825
V. Shevelev, Process of "primoverization" of numbers of the form a^n-1, arXiv:0807.2332 [math.NT], 2008.
S. Wagstaff, Factorizations of 2^n-1
EXAMPLE
Entry 3 from (q=2,p=3), entry 11 from (q=2,p=5), entry 43 from (q=2,p=7), entry 151 from (q=3,p=5), entry 683 from (q=2,p=11).
MAPLE
N:= 100: # to use all (p, q) with p*q < N
Primes:= select(isprime, [$2..floor(N/2)]):
A:= {}:
for i from 1 to nops(Primes) do
p:= Primes[i];
Qs:= select(q -> q < N/p, [seq(Primes[j], j=1..i-1)]);
A:= A union {seq((2^(p*q)-1)/(2^p-1)/(2^q-1), q=Qs)};
od:
A; # Robert Israel, Sep 02 2014
MATHEMATICA
terms = 27; Clear[seq]; seq[m_] := seq[m] = Table[(2^(p q)-1)/((2^p-1) (2^q-1)), {q, Prime[Range[m]]}, {p, Prime[Range[PrimePi[q]+1, terms]]}] // Flatten // Union // PadRight[#, terms]&;
seq[1]; seq[m=2]; While[seq[m] != seq[m-1], m++]; seq[m] (* Jean-François Alcover, Sep 17 2018 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Jul 15 2008, Jul 22 2008; corrected Sep 07 2008
EXTENSIONS
a(17) to a(27) from Robert Israel, Sep 03 2014
STATUS
approved