21613643 has 4 divisors (see below), whose sum is σ = 21648528. Its totient is φ = 21578760.

The previous prime is 21613639. The next prime is 21613663. The reversal of 21613643 is 34631612.

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 21613643 - 2² = 21613639 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21613663) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16496 + ... + 17757.

It is an arithmetic number, because the mean of its divisors is an integer number (5412132).

Almost surely, 2^21613643 is an apocalyptic number.

21613643 is a deficient number, since it is larger than the sum of its proper divisors (34885).

21613643 is an equidigital number, since it uses as much as digits as its factorization.

21613643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34884.

The product of its digits is 2592, while the sum is 26.

The square root of 21613643 is about 4649.0475368617. The cubic root of 21613643 is about 278.5539521174.

The spelling of 21613643 in words is "twenty-one million, six hundred thirteen thousand, six hundred forty-three".