21210721505436 has 96 divisors (see below), whose sum is σ = 53852903372800. Its totient is φ = 6472910050560.

The previous prime is 21210721505399. The next prime is 21210721505437. The reversal of 21210721505436 is 63450512701212.

It is a junction number, because it is equal to n+sod(n) for n = 21210721505394 and 21210721505403.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21210721505437) by changing a digit.

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 31 ways as a sum of consecutive naturals, for example, 2894886 + ... + 7127538.

Almost surely, 2^{21210721505436} is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21210721505436, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26926451686400).

21210721505436 is an abundant number, since it is smaller than the sum of its proper divisors (32642181867364).

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

21210721505436 is a wasteful number, since it uses less digits than its factorization.

21210721505436 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4233419 (or 4233417 counting only the distinct ones).

The product of its (nonzero) digits is 100800, while the sum is 39.

The spelling of 21210721505436 in words is "twenty-one trillion, two hundred ten billion, seven hundred twenty-one million, five hundred five thousand, four hundred thirty-six".