21720825 has 48 divisors (see below), whose sum is σ = 45612160. Its totient is φ = 9927360.

The previous prime is 21720821. The next prime is 21720827. The reversal of 21720825 is 52802712.

It is not a de Polignac number, because 21720825 - 2² = 21720821 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21720821) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 2427 + ... + 7023.

Almost surely, 2^21720825 is an apocalyptic number.

21720825 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21720825 is an abundant number, since it is smaller than the sum of its proper divisors (23891335).

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

21720825 is a wasteful number, since it uses less digits than its factorization.

21720825 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4623 (or 4612 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The square root of 21720825 is about 4660.5605885988. The cubic root of 21720825 is about 279.0136425286.

The spelling of 21720825 in words is "twenty-one million, seven hundred twenty thousand, eight hundred twenty-five".