Number Play

Natural numbers can sometimes be written

Natural numbers can sometimes be written as sums of consecutive numbers in more than one way. For example, 15 can be written as 7 + 8, 4 + 5 + 6, and

Parity means whether a number

Parity means whether a number is even or odd. Odd plus odd gives even, even plus even gives even, and odd plus even gives odd. For expressions formed

In an expression like a +

In an expression like a + b - c - d, changing one sign changes the value by an even number. For example, changing +b to -b changes the value by 2b, wh

A number is divisible by 10

A number is divisible by 10 if its units digit is 0. This works because every place value except the units place is a multiple of 10.

A 5

A 5-digit number in the Indian system can be written as e × 10000 + d × 1000 + c × 100 + b × 10 + a. More generally, a number can be expanded as ... +