21809956 has 12 divisors (see below), whose sum is σ = 43619968. Its totient is φ = 9347112.

The previous prime is 21809951. The next prime is 21809971. The reversal of 21809956 is 65990812.

21809956 is an admirable number.

It is not an unprimeable number, because it can be changed into a prime (21809951) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 389436 + ... + 389491.

Almost surely, 2^21809956 is an apocalyptic number.

It is an amenable number.

21809956 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21809956 is a wasteful number, since it uses less digits than its factorization.

21809956 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 778938 (or 778936 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 21809956 is about 4670.1130607299. The cubic root of 21809956 is about 279.3947641195.

The spelling of 21809956 in words is "twenty-one million, eight hundred nine thousand, nine hundred fifty-six".