21510665020 has 96 divisors (see below), whose sum is σ = 50299232256. Its totient is φ = 7673529600.

The previous prime is 21510665009. The next prime is 21510665089. The reversal of 21510665020 is 2056601512.

It is a self number, because there is not a number n which added to its sum of digits gives 21510665020.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5857785 + ... + 5861455.

It is an arithmetic number, because the mean of its divisors is an integer number (523950336).

Almost surely, 2^21510665020 is an apocalyptic number.

21510665020 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 21510665020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25149616128).

21510665020 is an abundant number, since it is smaller than the sum of its proper divisors (28788567236).

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

21510665020 is a wasteful number, since it uses less digits than its factorization.

21510665020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4451 (or 4449 counting only the distinct ones).

The product of its (nonzero) digits is 3600, while the sum is 28.

It can be divided in two parts, 215106 and 65020, that added together give a triangular number (280126 = T₇₄₈).

The spelling of 21510665020 in words is "twenty-one billion, five hundred ten million, six hundred sixty-five thousand, twenty".