40 when written "forty" is the only number with letters in alphabetical order, while "one" is the only one with letters in reverse order.
Pi (3.14159...) is a number that cannot be written as a fraction.sciensational.com Submitted by: Tiff - Witherbee, United States
The opposite sides of a dice cube always add up to seven. Submitted by: Ramesh - Pune, India
21978 when multiplied by 4 is the same number with digits in reverse order:
21978 × 4 = 87912
If you add up the numbers 1-100 consecutively (1+2+3+4+5...) the total is 5050.
The billionth digit of Pi is 9.
1 and 2 are the only numbers where they are the values of the numbers of factors they have.sciensational.com
2 and 5 are the only prime numbers that end in 2 or 5.
The largest known prime number (so far) is 17,425,170 digits long. Submitted by: Mathguy
The digits to the right of the Pi's (3.141...) decimal point can keep going forever, and there is no pattern to these digits at all.