Problem #112 says: Working from left-to-right if no digit is exceeded by the digit to its left it is called an increasing number; for example, 134468. Similarly if no digit is exceeded by the digit to its right it is called a decreasing number; for...

Problem #145 says: Some positive integers n have the property that the sum

Problem #206 says: Find the unique positive integer whose square has the form 1_2_3_4_5_6_7_8_9_0, where each “_” is a single digit. The range of number to check can be narrowed down with a calculator and some common sense. Then its just a square...

Problem #92 says:

Problem #188 says: The hyperexponentiation or tetration of a number a by a positive integer b, denoted by a↑↑b or ^(b)a, is recursively defined by: a↑↑1 = a, a↑↑(k+1) = a^((a↑↑k)). Thus we have e.g. 3↑↑2 = 3^(3) = 27, hence...