21208818280 has 64 divisors (see below), whose sum is σ = 51471579600. Its totient is φ = 7818608640.

The previous prime is 21208818277. The next prime is 21208818307. The reversal of 21208818280 is 8281880212.

It can be written as a sum of positive squares in 8 ways, for example, as 8690341284 + 12518476996 = 93222^2 + 111886^2 .

It is a Harshad number since it is a multiple of its sum of digits (40).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 301506 + ... + 365134.

Almost surely, 2^21208818280 is an apocalyptic number.

21208818280 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 21208818280, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25735789800).

21208818280 is an abundant number, since it is smaller than the sum of its proper divisors (30262761320).

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

21208818280 is a wasteful number, since it uses less digits than its factorization.

21208818280 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64294 (or 64290 counting only the distinct ones).

The product of its (nonzero) digits is 32768, while the sum is 40.

The spelling of 21208818280 in words is "twenty-one billion, two hundred eight million, eight hundred eighteen thousand, two hundred eighty".