问题描述：

The number 3797 has an interesting property. Being prime itself, it is possible to continuously remove digits from left to right, and remain prime at each stage: 3797, 797, 97, and 7. Similarly we can work from right to left: 3797, 379, 37, and 3.

Find the sum of the only eleven primes that are both truncatable from left to right and right to left.

NOTE: 2, 3, 5, and 7 are not considered to be truncatable primes.

1. 把数字从前向后依次截取

2.把数字从后向前依次截取

3.如果都是素数，返回true

实现：

(function(){

//truncate prime

var isTp = function(n){

var strN = n.toString();

for(var d = 0 ;d < strN.length; d++){
var s = strN.substr(0,d);
var s1 = strN.substr(strN.length-1-d,d+1);

var ns = parseInt(s);
var ns1 = parseInt(s1);
for(var i = 2 ;i < ns; i++){
if(ns%i == 0 ) {return false;}
}

for(var i = 2 ;i < ns1; i++){
if(ns1%i == 0 ) {return false;}
}

}


return true;
}

// find out the element that have 11 primes included all truncated  numbers 
for(var i = 10; i< 999999; i++){
if(isTp(i)) {console.log("===============" + i+ "=================");}
}

})();