21505464 has 24 divisors (see below), whose sum is σ = 58244160. Its totient is φ = 7168464.

The previous prime is 21505447. The next prime is 21505469. The reversal of 21505464 is 46450512.

It is a tau number, because it is divible by the number of its divisors (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505469) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 149272 + ... + 149415.

It is an arithmetic number, because the mean of its divisors is an integer number (2426840).

Almost surely, 2^21505464 is an apocalyptic number.

21505464 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21505464 is an abundant number, since it is smaller than the sum of its proper divisors (36738696).

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

21505464 is a wasteful number, since it uses less digits than its factorization.

21505464 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 298699 (or 298692 counting only the distinct ones).

The product of its (nonzero) digits is 4800, while the sum is 27.

The square root of 21505464 is about 4637.3984085907. The cubic root of 21505464 is about 278.0884420913.

Adding to 21505464 its reverse (46450512), we get a palindrome (67955976).

The spelling of 21505464 in words is "twenty-one million, five hundred five thousand, four hundred sixty-four".