21521766420 has 864 divisors, whose sum is σ = 90113587200. Its totient is φ = 4187842560.

The previous prime is 21521766389. The next prime is 21521766499. The reversal of 21521766420 is 2466712512.

It is a happy number.

21521766420 is a `hidden beast` number, since 2 + 1 + 5 + 2 + 1 + 7 + 6 + 642 + 0 = 666.

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 pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 287 ways as a sum of consecutive naturals, for example, 108149481 + ... + 108149679.

Almost surely, 2^21521766420 is an apocalyptic number.

21521766420 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 21521766420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45056793600).

21521766420 is an abundant number, since it is smaller than the sum of its proper divisors (68591820780).

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

21521766420 is a wasteful number, since it uses less digits than its factorization.

21521766420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 275 (or 244 counting only the distinct ones).

The product of its (nonzero) digits is 40320, while the sum is 36.

The spelling of 21521766420 in words is "twenty-one billion, five hundred twenty-one million, seven hundred sixty-six thousand, four hundred twenty".