251221920 has 144 divisors (see below), whose sum is σ = 841101408. Its totient is φ = 63016960.

The previous prime is 251221913. The next prime is 251221921. The reversal of 251221920 is 29122152.

It is a super-2 number, since 2×251221920² = 126224906176972800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is not an unprimeable number, because it can be changed into a prime (251221921) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 137815 + ... + 139625.

It is an arithmetic number, because the mean of its divisors is an integer number (5840982).

Almost surely, 2^251221920 is an apocalyptic number.

251221920 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 251221920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (420550704).

251221920 is an abundant number, since it is smaller than the sum of its proper divisors (589879488).

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

251221920 is a wasteful number, since it uses less digits than its factorization.

251221920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1863 (or 1838 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 24.

The square root of 251221920 is about 15849.9817034595. The cubic root of 251221920 is about 630.9852058051.

The spelling of 251221920 in words is "two hundred fifty-one million, two hundred twenty-one thousand, nine hundred twenty".