21613538 has 4 divisors (see below), whose sum is σ = 32420310. Its totient is φ = 10806768.

The previous prime is 21613517. The next prime is 21613577. The reversal of 21613538 is 83531612.

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

It can be written as a sum of positive squares in only one way, i.e., 20043529 + 1570009 = 4477^2 + 1253^2 .

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21613538.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5403383 + ... + 5403386.

Almost surely, 2^21613538 is an apocalyptic number.

21613538 is a deficient number, since it is larger than the sum of its proper divisors (10806772).

21613538 is a wasteful number, since it uses less digits than its factorization.

21613538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10806771.

The product of its digits is 4320, while the sum is 29.

The square root of 21613538 is about 4649.0362442123. The cubic root of 21613538 is about 278.5535010410.

The spelling of 21613538 in words is "twenty-one million, six hundred thirteen thousand, five hundred thirty-eight".