21508397820 has 288 divisors, whose sum is σ = 81131826048. Its totient is φ = 4490919936.

The previous prime is 21508397819. The next prime is 21508397873. The reversal of 21508397820 is 2879380512.

It is a happy number.

21508397820 is a `hidden beast` number, since 21 + 508 + 39 + 78 + 20 = 666.

It is a super-2 number, since 2×21508397820² (a number of 21 digits) contains 22 as substring.

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 95 ways as a sum of consecutive naturals, for example, 1582092 + ... + 1595628.

Almost surely, 2^21508397820 is an apocalyptic number.

21508397820 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 21508397820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40565913024).

21508397820 is an abundant number, since it is smaller than the sum of its proper divisors (59623428228).

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

21508397820 is a wasteful number, since it uses less digits than its factorization.

21508397820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13669 (or 13664 counting only the distinct ones).

The product of its (nonzero) digits is 241920, while the sum is 45.

The spelling of 21508397820 in words is "twenty-one billion, five hundred eight million, three hundred ninety-seven thousand, eight hundred twenty".