20891638 has 4 divisors (see below), whose sum is σ = 31337460. Its totient is φ = 10445818.

The previous prime is 20891603. The next prime is 20891639. The reversal of 20891638 is 83619802.

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

It is a junction number, because it is equal to n+sod(n) for n = 20891597 and 20891606.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20891639) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5222908 + ... + 5222911.

It is an arithmetic number, because the mean of its divisors is an integer number (7834365).

Almost surely, 2^20891638 is an apocalyptic number.

20891638 is a deficient number, since it is larger than the sum of its proper divisors (10445822).

20891638 is a wasteful number, since it uses less digits than its factorization.

20891638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10445821.

The product of its (nonzero) digits is 20736, while the sum is 37.

The square root of 20891638 is about 4570.7371396745. The cubic root of 20891638 is about 275.4170553430.

The spelling of 20891638 in words is "twenty million, eight hundred ninety-one thousand, six hundred thirty-eight".