251561520 has 480 divisors, whose sum is σ = 1058503680. Its totient is φ = 52254720.

The previous prime is 251561509. The next prime is 251561521. The reversal of 251561520 is 25165152.

251561520 is a `hidden beast` number, since 2 + 51 + 561 + 52 + 0 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (251561521) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 3543085 + ... + 3543155.

It is an arithmetic number, because the mean of its divisors is an integer number (2205216).

Almost surely, 2^251561520 is an apocalyptic number.

251561520 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 251561520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (529251840).

251561520 is an abundant number, since it is smaller than the sum of its proper divisors (806942160).

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

251561520 is a wasteful number, since it uses less digits than its factorization.

251561520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153 (or 144 counting only the distinct ones).

The product of its (nonzero) digits is 3000, while the sum is 27.

The square root of 251561520 is about 15860.6910316039. The cubic root of 251561520 is about 631.2693982210.

The spelling of 251561520 in words is "two hundred fifty-one million, five hundred sixty-one thousand, five hundred twenty".