21691572 has 24 divisors (see below), whose sum is σ = 57844416. Its totient is φ = 6197568.

The previous prime is 21691547. The next prime is 21691577. The reversal of 21691572 is 27519612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21691577) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 129033 + ... + 129200.

It is an arithmetic number, because the mean of its divisors is an integer number (2410184).

Almost surely, 2^21691572 is an apocalyptic number.

It is an amenable number.

21691572 is an abundant number, since it is smaller than the sum of its proper divisors (36152844).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21691572 is a wasteful number, since it uses less digits than its factorization.

21691572 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 258247 (or 258245 counting only the distinct ones).

The product of its digits is 7560, while the sum is 33.

The square root of 21691572 is about 4657.4211748563. The cubic root of 21691572 is about 278.8883303311. Note that the first 3 decimals are identical.

It can be divided in two parts, 2169 and 1572, that added together give a triangular number (3741 = T₈₆).

The spelling of 21691572 in words is "twenty-one million, six hundred ninety-one thousand, five hundred seventy-two".