21291090 has 16 divisors (see below), whose sum is σ = 51098688. Its totient is φ = 5677616.

The previous prime is 21291029. The next prime is 21291091. The reversal of 21291090 is 9019212.

It is a self number, because there is not a number n which added to its sum of digits gives 21291090.

It is not an unprimeable number, because it can be changed into a prime (21291091) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 354822 + ... + 354881.

It is an arithmetic number, because the mean of its divisors is an integer number (3193668).

Almost surely, 2^21291090 is an apocalyptic number.

21291090 is an abundant number, since it is smaller than the sum of its proper divisors (29807598).

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

21291090 is a wasteful number, since it uses less digits than its factorization.

21291090 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 709713.

The product of its (nonzero) digits is 324, while the sum is 24.

The square root of 21291090 is about 4614.2269124957. The cubic root of 21291090 is about 277.1613269554.

The spelling of 21291090 in words is "twenty-one million, two hundred ninety-one thousand, ninety".