OFFSET
1,2
LINKS
Michael B. Porter, Table of n, a(n) for n = 1..60 with data from Thomas Ordowski, Marek Wolf, and Joerg Arndt; contains all terms <= 10^4.
EXAMPLE
6 is in the sequence because 6 + 6#/6 = 6 + 5#/6 = 6 + 30/6 = 11 is prime.
4 is not in the sequence because 4 + 4#/4 = 4 + 6/4 = 11/2 is not an integer.
11 is not in the sequence because 11 + 11#/11 = 11 + 7# = 11 + 210 = 221 is not prime (221 = 13 * 17).
PROG
(PARI)
pp(n) = { my(r=1); forprime(p=2, n, r*=p); r; }
/* we need to take care about n+pp(n)/n not always being integral: */
is(n) = { my(r=n+pp(n)/n); return( (type(r)==type(1)) && ispseudoprime(r) ); }
for (n=1, 10^4, if ( is(n), print1(n, ", ") ) );
/* Joerg Arndt, Apr 14 2013 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Thomas Ordowski, Apr 13 2013
EXTENSIONS
a(22)-a(35) from Marek Wolf, Apr 14 2013
a(36)-a(54) from Joerg Arndt, Apr 14 2013
STATUS
approved