21993547 has 4 divisors (see below), whose sum is σ = 22074976. Its totient is φ = 21912120.

The previous prime is 21993541. The next prime is 21993581. The reversal of 21993547 is 74539912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21993547 - 2¹¹ = 21991499 is a prime.

It is a super-2 number, since 2×21993547² = 967432219282418, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21993541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40308 + ... + 40849.

It is an arithmetic number, because the mean of its divisors is an integer number (5518744).

Almost surely, 2^21993547 is an apocalyptic number.

21993547 is a deficient number, since it is larger than the sum of its proper divisors (81429).

21993547 is an equidigital number, since it uses as much as digits as its factorization.

21993547 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81428.

The product of its digits is 68040, while the sum is 40.

The square root of 21993547 is about 4689.7278172619. The cubic root of 21993547 is about 280.1765340838.

The spelling of 21993547 in words is "twenty-one million, nine hundred ninety-three thousand, five hundred forty-seven".