21909690 has 80 divisors (see below), whose sum is σ = 64294560. Its totient is φ = 5309280.

The previous prime is 21909673. The next prime is 21909691. The reversal of 21909690 is 9690912.

It is a super-2 number, since 2×21909690² = 960069031792200, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21909691) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 7681 + ... + 10139.

It is an arithmetic number, because the mean of its divisors is an integer number (803682).

Almost surely, 2^21909690 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21909690, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32147280).

21909690 is an abundant number, since it is smaller than the sum of its proper divisors (42384870).

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

21909690 is a wasteful number, since it uses less digits than its factorization.

21909690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2489 (or 2480 counting only the distinct ones).

The product of its (nonzero) digits is 8748, while the sum is 36.

The square root of 21909690 is about 4680.7787813568. The cubic root of 21909690 is about 279.8199948481.

The spelling of 21909690 in words is "twenty-one million, nine hundred nine thousand, six hundred ninety".