21211615720 has 16 divisors (see below), whose sum is σ = 47726135460. Its totient is φ = 8484646272.

The previous prime is 21211615699. The next prime is 21211615753. The reversal of 21211615720 is 2751611212.

It can be written as a sum of positive squares in 2 ways, for example, as 19527826564 + 1683789156 = 139742^2 + 41034^2 .

It is a super-2 number, since 2×21211615720² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 265145157 + ... + 265145236.

Almost surely, 2^21211615720 is an apocalyptic number.

21211615720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21211615720 is an abundant number, since it is smaller than the sum of its proper divisors (26514519740).

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

21211615720 is a wasteful number, since it uses less digits than its factorization.

21211615720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 530290404 (or 530290400 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 28.

The spelling of 21211615720 in words is "twenty-one billion, two hundred eleven million, six hundred fifteen thousand, seven hundred twenty".