21391625 has 16 divisors (see below), whose sum is σ = 28104960. Its totient is φ = 16210800.

The previous prime is 21391621. The next prime is 21391649. The reversal of 21391625 is 52619312.

It is not a de Polignac number, because 21391625 - 2² = 21391621 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21391621) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2129 + ... + 6878.

It is an arithmetic number, because the mean of its divisors is an integer number (1756560).

Almost surely, 2^21391625 is an apocalyptic number.

21391625 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21391625 is a deficient number, since it is larger than the sum of its proper divisors (6713335).

21391625 is an equidigital number, since it uses as much as digits as its factorization.

21391625 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9041 (or 9031 counting only the distinct ones).

The product of its digits is 3240, while the sum is 29.

The square root of 21391625 is about 4625.1081068446. The cubic root of 21391625 is about 277.5968874140.

The spelling of 21391625 in words is "twenty-one million, three hundred ninety-one thousand, six hundred twenty-five".