252

252 = 2 x 2 x 3 x 3 x 7.

252 is the smallest number that is the product of two distinct numbers that are reverse of each other: 252 = 12 x 21.

252 = 2⁸ - 4.

252 is the third value of Ramanujan's tau function (A000594).

252 is a hexagonal pyramidal number.

If you flip a coin 10 times in a row, there are exactly 252 ways in which it can turn out that you get exactly five heads and five tails.

Source: Number Gossip

946

946 = 2 x 11 x 43.

946 is the 43rd triangular number (A000217). It is the sum of all integers from 1 to 43.

946 is also a hexagonal number (A000384), a centered nonagonal number, and a hexagonal pyramidal number (A002412).

946 is the only three-digit number such that the reversal of the concatenation of the first 946 natural numbers is a prime.

946 is the largest known number n such that n is the sum of two consecutive primes but not the sum of two sums of two consecutive primes.

Source: Prime Curios!

161

161 = 7 x 23.

161 is a divisor of 22² - 1.

161 is a hexagonal pyramidal number.

161 is a Cullen number.

Every number greater than 161 is the sum of distinct primes of the form 6n - 1.

161 is the smallest semiprime that yields a palindromic prime (191) when turned upside down.

161 is the sum of five consecutive prime numbers: 161 = 23 + 29 + 31 + 37 + 41.

There are 161 ways to bet on a roulette wheel.

Source: Prime Curios!

715

715 = 5 x 11 x 13.

715 is the tenth pentatope number. It is also a pentagonal number (A000326), a hendecagonal number (A051682), and a hexagonal pyramidal number (A002412).

715 is 222111 in base 3, 23023 in base 4, and 1313 in base 8.

715 is the number of intersections of diagonals in the interior of a regular 13-gon (A006561).

715 is the smallest positive number that can be written as a sum of distinct Fibonacci numbers in 26 ways.

Source: Number Gossip

525

525 = 3 x 5² x 7.

525 in base 6 is 2233.

525 is a hexagonal pyramidal number (greengrocer's number).

525 is a number with exactly 12 divisors: 1, 3, 5, 7, 15, 21, 25, 35, 75, 105, 175, 525.


Dionysius Exiguus produced his tables for computing the date of Easter in the year 525.

Source: The Positive Integers