21537664 has 16 divisors (see below), whose sum is σ = 42907320. Its totient is φ = 10768768.

The previous prime is 21537661. The next prime is 21537667. The reversal of 21537664 is 46673512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21537661) and next prime (21537667).

It is a tau number, because it is divible by the number of its divisors (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21537661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 84004 + ... + 84259.

Almost surely, 2^21537664 is an apocalyptic number.

It is an amenable number.

21537664 is a deficient number, since it is larger than the sum of its proper divisors (21369656).

21537664 is an equidigital number, since it uses as much as digits as its factorization.

21537664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 168277 (or 168265 counting only the distinct ones).

The product of its digits is 30240, while the sum is 34.

The square root of 21537664 is about 4640.8688841638. The cubic root of 21537664 is about 278.2271662531.

It can be divided in two parts, 21537 and 664, that added together give a square (22201 = 149²).

The spelling of 21537664 in words is "twenty-one million, five hundred thirty-seven thousand, six hundred sixty-four".