OFFSET
1,1
COMMENTS
This sequence has not been proved to be infinite.
The terms p such that 2^p - 1 is a Mersenne prime are 2, 3, 5, 7, and 13.
If p is prime, then gpf(lpf(2^p - 1) - 1) >= p.
Primes q such that gpf(lpf(2^q - 1) - 1) > q are A292237.
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..119
EXAMPLE
We have gpf(lpf(2^11 - 1) - 1) = gpf(23 - 1) = 11, so 11 is a term.
MATHEMATICA
lpf[n_] := FactorInteger[n][[1, 1]]; gpf[n_] := FactorInteger[n][[-1, 1]]; Select[ Prime@ Range@ 45, gpf[lpf[2^# - 1] - 1] == # &] (* Giovanni Resta, Aug 30 2017 *)
PROG
(PARI) listp(nn) = forprime(p=2, nn, if (vecmax(factor(vecmin(factor(2^p-1)[, 1])-1)[, 1]) == p, print1(p, ", ")); ); \\ Michel Marcus, Aug 30 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Aug 30 2017
EXTENSIONS
a(17)-a(26) from Michel Marcus, Aug 30 2017
a(27)-a(34) from Giovanni Resta, Aug 30 2017
a(35)-a(52) from Charles R Greathouse IV, Aug 30 2017
STATUS
approved