Numbers expressible as sum of two powers of primes in more than one way: n=p^a+q^b=r^c+s^q=..., p,q,r,s,... are (distinct) primes and a,b,c,d,... >=1. Just 3 examples: 17=2^2+13^1=2^3+3^2 33=2^3+5^2=2^4+17^1=2^2+29^2 2200=3^7+13^1=3^1+13^3 Old hat? More terms? -- Zak Seidov