21851380 has 48 divisors (see below), whose sum is σ = 48666240. Its totient is φ = 8224128.

The previous prime is 21851377. The next prime is 21851383. The reversal of 21851380 is 8315812.

It is an interprime number because it is at equal distance from previous prime (21851377) and next prime (21851383).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21851383) 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, 30466 + ... + 31174.

It is an arithmetic number, because the mean of its divisors is an integer number (1013880).

Almost surely, 2^21851380 is an apocalyptic number.

21851380 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 21851380, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24333120).

21851380 is an abundant number, since it is smaller than the sum of its proper divisors (26814860).

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

21851380 is a wasteful number, since it uses less digits than its factorization.

21851380 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 808 (or 806 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 28.

The square root of 21851380 is about 4674.5459672571. The cubic root of 21851380 is about 279.5715385720.

The spelling of 21851380 in words is "twenty-one million, eight hundred fifty-one thousand, three hundred eighty".