21809964 has 48 divisors (see below), whose sum is σ = 55996416. Its totient is φ = 6552000.

The previous prime is 21809951. The next prime is 21809971. The reversal of 21809964 is 46990812.

It is a super-3 number, since 3×21809964³ (a number of 23 digits) contains 333 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 16114 + ... + 17414.

It is an arithmetic number, because the mean of its divisors is an integer number (1166592).

Almost surely, 2^21809964 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21809964, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27998208).

21809964 is an abundant number, since it is smaller than the sum of its proper divisors (34186452).

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

21809964 is a wasteful number, since it uses less digits than its factorization.

21809964 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1446 (or 1444 counting only the distinct ones).

The product of its (nonzero) digits is 31104, while the sum is 39.

The square root of 21809964 is about 4670.1139172401. The cubic root of 21809964 is about 279.3947982806.

The spelling of 21809964 in words is "twenty-one million, eight hundred nine thousand, nine hundred sixty-four".