What are the first and the last 20 digits of: 7^7^7^7? Any help or hint would be appreciated. Thank you.
first 20 digits: 73897156067403508131
last 20: 33408341373887572343
please correct me if i'm wrong :)
No, that is not correct! You must calculate from the RIGHT to LEFT, and not from LEFT to RIGHT.
7^7^7^7 =7^7^823,543 =7^[3.7598....x 10^695974 ]
The first 20 digits are = 7^7^7^7 =7^7^823,543 = 72,390,474,974,388,824,254
The last 20 digits are = 7^7^7^7 mod 10^20 =82,879,357,182,733,172,343
+111 
