21216635540 has 24 divisors (see below), whose sum is σ = 44575088712. Its totient is φ = 8482815360.

The previous prime is 21216635537. The next prime is 21216635603. The reversal of 21216635540 is 4553661212.

It can be written as a sum of positive squares in 4 ways, for example, as 9378760336 + 11837875204 = 96844^2 + 108802^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21216635540.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 194399 + ... + 283238.

It is an arithmetic number, because the mean of its divisors is an integer number (1857295363).

Almost surely, 2^21216635540 is an apocalyptic number.

21216635540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21216635540 is an abundant number, since it is smaller than the sum of its proper divisors (23358453172).

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

21216635540 is a wasteful number, since it uses less digits than its factorization.

21216635540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 479867 (or 479865 counting only the distinct ones).

The product of its (nonzero) digits is 43200, while the sum is 35.

The spelling of 21216635540 in words is "twenty-one billion, two hundred sixteen million, six hundred thirty-five thousand, five hundred forty".