21386820 has 96 divisors (see below), whose sum is σ = 73721088. Its totient is φ = 4511232.

The previous prime is 21386819. The next prime is 21386821. The reversal of 21386820 is 2868312.

It is an interprime number because it is at equal distance from previous prime (21386819) and next prime (21386821).

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

It is not an unprimeable number, because it can be changed into a prime (21386821) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 3502 + ... + 7418.

It is an arithmetic number, because the mean of its divisors is an integer number (767928).

Almost surely, 2^21386820 is an apocalyptic number.

21386820 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 21386820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36860544).

21386820 is an abundant number, since it is smaller than the sum of its proper divisors (52334268).

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

21386820 is a wasteful number, since it uses less digits than its factorization.

21386820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3949 (or 3947 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 30.

The square root of 21386820 is about 4624.5886303541. The cubic root of 21386820 is about 277.5761011962.

The spelling of 21386820 in words is "twenty-one million, three hundred eighty-six thousand, eight hundred twenty".