21505764 has 24 divisors (see below), whose sum is σ = 57348928. Its totient is φ = 6144480.

The previous prime is 21505763. The next prime is 21505787. The reversal of 21505764 is 46750512.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21505763) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 127927 + ... + 128094.

Almost surely, 2^21505764 is an apocalyptic number.

It is an amenable number.

21505764 is an abundant number, since it is smaller than the sum of its proper divisors (35843164).

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

21505764 is a wasteful number, since it uses less digits than its factorization.

21505764 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 256035 (or 256033 counting only the distinct ones).

The product of its (nonzero) digits is 8400, while the sum is 30.

The square root of 21505764 is about 4637.4307542000. The cubic root of 21505764 is about 278.0897351913.

The spelling of 21505764 in words is "twenty-one million, five hundred five thousand, seven hundred sixty-four".