21012090 has 64 divisors (see below), whose sum is σ = 56391552. Its totient is φ = 4966400.

The previous prime is 21012077. The next prime is 21012091. The reversal of 21012090 is 9021012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is not an unprimeable number, because it can be changed into a prime (21012091) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 12754 + ... + 14306.

It is an arithmetic number, because the mean of its divisors is an integer number (881118).

Almost surely, 2^21012090 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21012090, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28195776).

21012090 is an abundant number, since it is smaller than the sum of its proper divisors (35379462).

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

21012090 is a wasteful number, since it uses less digits than its factorization.

21012090 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1615.

The product of its (nonzero) digits is 36, while the sum is 15.

The square root of 21012090 is about 4583.8946322969. The cubic root of 21012090 is about 275.9453525497.

The spelling of 21012090 in words is "twenty-one million, twelve thousand, ninety".