%N Primes from composite numbers by prefixing with 1.
%C The composite numbers are considered in increasing order.
%H Dario Alpern, <a href="http://www.alpertron.com.ar/ECM.HTM">Factorization using the Elliptic Curve Method</a>
%e 1493 is a prime from the composite number 493 by prefixing it with 1.
%Y Cf. A002808
%A _Parthasarathy Nambi_, Aug 30 2009