21390891840 has 168 divisors, whose sum is σ = 76113147240. Its totient is φ = 5507518464.

The previous prime is 21390891833. The next prime is 21390891853. The reversal of 21390891840 is 4819809312.

21390891840 is a `hidden beast` number, since 2 + 1 + 390 + 89 + 184 + 0 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 9064563264 + 12326328576 = 95208^2 + 111024^2 .

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 44539 + ... + 211578.

Almost surely, 2^21390891840 is an apocalyptic number.

21390891840 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 21390891840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38056573620).

21390891840 is an abundant number, since it is smaller than the sum of its proper divisors (54722255400).

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

21390891840 is a wasteful number, since it uses less digits than its factorization.

21390891840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 256169 (or 256156 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 45.

The spelling of 21390891840 in words is "twenty-one billion, three hundred ninety million, eight hundred ninety-one thousand, eight hundred forty".