21206405880 has 448 divisors, whose sum is σ = 82654408800. Its totient is φ = 4837294080.

The previous prime is 21206405849. The next prime is 21206405911. The reversal of 21206405880 is 8850460212.

21206405880 is a `hidden beast` number, since 2 + 1 + 2 + 0 + 640 + 5 + 8 + 8 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (21206405849) and next prime (21206405911).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 111 ways as a sum of consecutive naturals, for example, 5450976 + ... + 5454864.

Almost surely, 2^21206405880 is an apocalyptic number.

21206405880 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 21206405880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41327204400).

21206405880 is an abundant number, since it is smaller than the sum of its proper divisors (61448002920).

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

21206405880 is a wasteful number, since it uses less digits than its factorization.

21206405880 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3946 (or 3927 counting only the distinct ones).

The product of its (nonzero) digits is 30720, while the sum is 36.

The spelling of 21206405880 in words is "twenty-one billion, two hundred six million, four hundred five thousand, eight hundred eighty".