21890090209 has 27 divisors (see below), whose sum is σ = 25058515923. Its totient is φ = 19110793104.

The previous prime is 21890090207. The next prime is 21890090221. The reversal of 21890090209 is 90209009812.

The square root of 21890090209 is 147953.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 3238179025 + 18651911184 = 56905^2 + 136572^2 .

It is not a de Polignac number, because 21890090209 - 2¹ = 21890090207 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21890090207) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 36544092 + ... + 36544690.

Almost surely, 2^21890090209 is an apocalyptic number.

21890090209 is the 147953-rd square number.

21890090209 is the 73977-th centered octagonal number.

It is an amenable number.

21890090209 is a deficient number, since it is larger than the sum of its proper divisors (3168425714).

21890090209 is an frugal number, since it uses more digits than its factorization.

21890090209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1262 (or 631 counting only the distinct ones).

The product of its (nonzero) digits is 23328, while the sum is 40.

The spelling of 21890090209 in words is "twenty-one billion, eight hundred ninety million, ninety thousand, two hundred nine".