OFFSET
1,1
COMMENTS
Surely these are infinite?
FORMULA
For digits d of n if d=6 make it 9 else if d=9 make it 6 and test for prime()
EXAMPLE
76 -> 79 prime
PROG
(PARI) flip69pr(n) = { for(x=1, n, y=x; v=0; f=0; ln =length(Str(x)); a = vector(ln); forstep(j=ln, 1, -1, r = y%10; a[j]=r; if(r==6, a[j] = 9; f=1); if(r==9, a[j] = 6; f=1); y = floor(y/10); ); forstep(j=ln, 1, -1, v=v+a[j]*10^(ln-j) ); if(isprime(v) && f, print1(v", ")); ) }
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Cino Hilliard, Nov 02 2003
STATUS
approved