21391860 has 144 divisors (see below), whose sum is σ = 72067968. Its totient is φ = 4642560.

The previous prime is 21391849. The next prime is 21391871. The reversal of 21391860 is 6819312.

It is an interprime number because it is at equal distance from previous prime (21391849) and next prime (21391871).

It is a super-2 number, since 2×21391860² = 915223348519200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 403594 + ... + 403646.

It is an arithmetic number, because the mean of its divisors is an integer number (500472).

Almost surely, 2^21391860 is an apocalyptic number.

21391860 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21391860, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36033984).

21391860 is an abundant number, since it is smaller than the sum of its proper divisors (50676108).

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

21391860 is a wasteful number, since it uses less digits than its factorization.

21391860 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 134 (or 101 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 21391860 is about 4625.1335115864. The cubic root of 21391860 is about 277.5979039338.

The spelling of 21391860 in words is "twenty-one million, three hundred ninety-one thousand, eight hundred sixty".