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Nordic
1991 Nordic
1
1
Part of
1991 Nordic
Problems
(1)
last 2 digits 2^5 + 2^{5^2}} + 2^{5^{3}} +... + 2^{5^{1991}}
Source: Nordic Mathematical Contest 1991 #1
10/5/2017
Determine the last two digits of the number
2
5
+
2
5
2
+
2
5
3
+
.
.
.
+
2
5
1991
2^5 + 2^{5^{2}} + 2^{5^{3}} +... + 2^{5^{1991}}
2
5
+
2
5
2
+
2
5
3
+
...
+
2
5
1991
, written in decimal notation.
Last digit
number theory