21372820 has 72 divisors (see below), whose sum is σ = 52945704. Its totient is φ = 7225344.

The previous prime is 21372811. The next prime is 21372839. The reversal of 21372820 is 2827312.

It can be written as a sum of positive squares in 4 ways, for example, as 414736 + 20958084 = 644^2 + 4578^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 110644 + ... + 110836.

It is an arithmetic number, because the mean of its divisors is an integer number (735357).

Almost surely, 2^21372820 is an apocalyptic number.

21372820 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 21372820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26472852).

21372820 is an abundant number, since it is smaller than the sum of its proper divisors (31572884).

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

21372820 is a wasteful number, since it uses less digits than its factorization.

21372820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 329 (or 320 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 21372820 is about 4623.0747344165. The cubic root of 21372820 is about 277.5155200583.

The spelling of 21372820 in words is "twenty-one million, three hundred seventy-two thousand, eight hundred twenty".