Posted by Chris on Monday, May 7, 2012 at 8:07am.
abcdef
a=b+4
c=f-1
de=af
Let's see what de can be, and what af could then be. Remember that a>=5, since b>=1
de: af
14: 72 b=3 c=1 no
15: 53 no, odd
16: 82 b=3 c=1 no
18: 92 b=5 c=1 no, or 63 b=2 c=1 no
21: 73 no, odd
24: 83 no, odd
27: 93 no, odd
28: 74 b=3 c=3 no
32: 84 b=4 no
36: 94 b=5 c=3 no
42: 67 no, odd; 76 b=3 c=5 YES
54: 69 no, odd; or 96 b=5 no
56: 78 b=3 c=7 no, or 87 b=4 c=6 no
63: 79 or 97 no, both odd
72: 89 no, odd; 98 b=5,c=7 no
So, we are left with 735426