21690380 has 48 divisors (see below), whose sum is σ = 48371904. Its totient is φ = 8152320.

The previous prime is 21690371. The next prime is 21690391. The reversal of 21690380 is 8309612.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27674 + ... + 28446.

It is an arithmetic number, because the mean of its divisors is an integer number (1007748).

Almost surely, 2^21690380 is an apocalyptic number.

21690380 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21690380, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24185952).

21690380 is an abundant number, since it is smaller than the sum of its proper divisors (26681524).

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

21690380 is a wasteful number, since it uses less digits than its factorization.

21690380 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 866 (or 864 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 21690380 is about 4657.2932052857. The cubic root of 21690380 is about 278.8832217267.

Adding to 21690380 its reverse (8309612), we get a palindrome (29999992).

The spelling of 21690380 in words is "twenty-one million, six hundred ninety thousand, three hundred eighty".