21451840 has 56 divisors (see below), whose sum is σ = 52303680. Its totient is φ = 8375808.

The previous prime is 21451831. The next prime is 21451849. The reversal of 21451840 is 4815412.

It is an interprime number because it is at equal distance from previous prime (21451831) and next prime (21451849).

It is not an unprimeable number, because it can be changed into a prime (21451849) 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, 12981 + ... + 14539.

Almost surely, 2^21451840 is an apocalyptic number.

21451840 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 21451840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26151840).

21451840 is an abundant number, since it is smaller than the sum of its proper divisors (30851840).

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

21451840 is a wasteful number, since it uses less digits than its factorization.

21451840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1619 (or 1609 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 25.

The square root of 21451840 is about 4631.6131099219. The cubic root of 21451840 is about 277.8571113253.

The spelling of 21451840 in words is "twenty-one million, four hundred fifty-one thousand, eight hundred forty".