21537648 has 60 divisors (see below), whose sum is σ = 65759928. Its totient is φ = 6526080.

The previous prime is 21537643. The next prime is 21537661. The reversal of 21537648 is 84673512.

21537648 is a `hidden beast` number, since 2 + 1 + 5 + 3 + 7 + 648 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21537641) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5215 + ... + 8382.

Almost surely, 2^21537648 is an apocalyptic number.

It is an amenable number.

21537648 is an abundant number, since it is smaller than the sum of its proper divisors (44222280).

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

21537648 is a wasteful number, since it uses less digits than its factorization.

21537648 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13622 (or 13613 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21537648 is about 4640.8671603484. The cubic root of 21537648 is about 278.2270973562.

It can be divided in two parts, 2153 and 7648, that added together give a square (9801 = 99²).

The spelling of 21537648 in words is "twenty-one million, five hundred thirty-seven thousand, six hundred forty-eight".