This number is a composite.
A brilliant number formed by taking the first six positive integers and raising successive pairs to powers as follows: 15707 = 113 * 139 = 1^2 + 3^4 + 5^6. Note also the very rare property that the reversal of this brilliant number is a different brilliant number: 70751 = 139 * 509. Shall we call this a tnaillirb? [Post]