What is the sum of all of the four-digit positive integers that can be written with the digits 1, 2, 3 and 4 if each digit must be used exactly once in each four-digit positive integer?
+129840 1234
1243
1324
1342
1423
1432
-------
7998
2134
2143
2314
2341
2413
2431
-------
13776
3124
3142
3214
3241
3412
3421
-------
19554
Notice........13776 - 7998 = 5778
And 19554 - 13776 = 5778
So.....we would speculate that the next sum = 19554 + 5778 = 25332
4123
4132
4213
4231
4312
4321
-------
25332
So....... 7998 + 13776 + 19554 + 25332 = 66660
