
COMMENTS

347, 457, 461 and 701 are also terms. The only other possible terms up to 1000 are 263, 311, 509, 557, 617, 647 and 991; repunits of these lengths are known to be composite but the linked sources do not provide their factors.  Rick L. Shepherd, Mar 11 2003
The Yousuke Koide reference now shows repunit of length 263 partially factored, no longer possible candidate for this sequence.  Ray Chandler, Sep 06 2005
The term 263 has 3 prime factors, 617 has one prime factor and a large composite. For terms between 1000 to 2000, other possible terms are 1117, 1213, 1259, 1291, 1373, 1447, 1607, 1637, 1663, 1669, 1759, 1823, 1949, 1987, 2063 & 2087.  Robert G. Wilson v, Apr 26 2010
All terms are either primes or squares of primes in A004023. In particular, the only composite below a million is 4.  Charles R Greathouse IV, Nov 21 2014
