21051023904 has 336 divisors, whose sum is σ = 66096376920. Its totient is φ = 6591932928.

The previous prime is 21051023893. The next prime is 21051023921. The reversal of 21051023904 is 40932015012.

It can be written as a sum of positive squares in 4 ways, for example, as 15830672400 + 5220351504 = 125820^2 + 72252^2 .

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 568946574 + ... + 568946610.

Almost surely, 2^21051023904 is an apocalyptic number.

21051023904 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 21051023904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33048188460).

21051023904 is an abundant number, since it is smaller than the sum of its proper divisors (45045353016).

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

21051023904 is an frugal number, since it uses more digits than its factorization.

21051023904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 152 (or 71 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

Adding to 21051023904 its reverse (40932015012), we get a palindrome (61983038916).

The spelling of 21051023904 in words is "twenty-one billion, fifty-one million, twenty-three thousand, nine hundred four".