21809970 has 96 divisors (see below), whose sum is σ = 69818112. Its totient is φ = 4599936.

The previous prime is 21809951. The next prime is 21809971. The reversal of 21809970 is 7990812.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21809971) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 6859 + ... + 9521.

It is an arithmetic number, because the mean of its divisors is an integer number (727272).

Almost surely, 2^21809970 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21809970, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34909056).

21809970 is an abundant number, since it is smaller than the sum of its proper divisors (48008142).

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

21809970 is a wasteful number, since it uses less digits than its factorization.

21809970 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2696 (or 2693 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 21809970 is about 4670.1145596227. The cubic root of 21809970 is about 279.3948239015.

The spelling of 21809970 in words is "twenty-one million, eight hundred nine thousand, nine hundred seventy".