21684537 has 48 divisors (see below), whose sum is σ = 39099520. Its totient is φ = 11632896.

The previous prime is 21684527. The next prime is 21684557. The reversal of 21684537 is 73548612.

It is not a de Polignac number, because 21684537 - 2⁴ = 21684521 is a prime.

It is a super-3 number, since 3×21684537³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21684517) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 54423 + ... + 54819.

Almost surely, 2^21684537 is an apocalyptic number.

21684537 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21684537 is a deficient number, since it is larger than the sum of its proper divisors (17414983).

21684537 is a wasteful number, since it uses less digits than its factorization.

21684537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 447 (or 424 counting only the distinct ones).

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

The square root of 21684537 is about 4656.6658673347. The cubic root of 21684537 is about 278.8581774289.

The spelling of 21684537 in words is "twenty-one million, six hundred eighty-four thousand, five hundred thirty-seven".