251621489664 has 440 divisors, whose sum is σ = 803433220128. Its totient is φ = 78246051840.

The previous prime is 251621489663. The next prime is 251621489671. The reversal of 251621489664 is 466984126152.

It is a happy number.

251621489664 is a `hidden beast` number, since 2 + 5 + 1 + 621 + 4 + 8 + 9 + 6 + 6 + 4 = 666.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a self number, because there is not a number n which added to its sum of digits gives 251621489664.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (251621489663) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 78214584 + ... + 78217800.

Almost surely, 2^251621489664 is an apocalyptic number.

251621489664 is a gapful number since it is divisible by the number (24) 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 251621489664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (401716610064).

251621489664 is an abundant number, since it is smaller than the sum of its proper divisors (551811730464).

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

251621489664 is a wasteful number, since it uses less digits than its factorization.

251621489664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3313 (or 3286 counting only the distinct ones).

The product of its digits is 4976640, while the sum is 54.

The spelling of 251621489664 in words is "two hundred fifty-one billion, six hundred twenty-one million, four hundred eighty-nine thousand, six hundred sixty-four".