MathDB

Last Two Digits and 21st Power

Source:

September 7, 2024

number theory2024

Problem Statement

Let

N \in \{10, 11, \ldots, 99\}

be a two-digit positive integer. Compute the number of values of

N

for which the last two digits in the decimal expansion of

N^{21}

are the digits of

N

in the same order.