21153990 has 64 divisors (see below), whose sum is σ = 59657472. Its totient is φ = 4732800.

The previous prime is 21153971. The next prime is 21154019. The reversal of 21153990 is 9935112.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a Curzon number.

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, 1825 + ... + 6755.

It is an arithmetic number, because the mean of its divisors is an integer number (932148).

Almost surely, 2^21153990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21153990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29828736).

21153990 is an abundant number, since it is smaller than the sum of its proper divisors (38503482).

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

21153990 is a wasteful number, since it uses less digits than its factorization.

21153990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4965.

The product of its (nonzero) digits is 2430, while the sum is 30.

The square root of 21153990 is about 4599.3466927380. The cubic root of 21153990 is about 276.5651358873.

It can be divided in two parts, 2115 and 3990, that added together give a triangular number (6105 = T₁₁₀).

The spelling of 21153990 in words is "twenty-one million, one hundred fifty-three thousand, nine hundred ninety".