20987791 has 4 divisors (see below), whose sum is σ = 22895784. Its totient is φ = 19079800.

The previous prime is 20987783. The next prime is 20987797. The reversal of 20987791 is 19778902.

It is a happy number.

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 20987791 - 2³ = 20987783 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20987797) 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, 953980 + ... + 954001.

It is an arithmetic number, because the mean of its divisors is an integer number (5723946).

Almost surely, 2^20987791 is an apocalyptic number.

20987791 is a deficient number, since it is larger than the sum of its proper divisors (1907993).

20987791 is a wasteful number, since it uses less digits than its factorization.

20987791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1907992.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 20987791 is about 4581.2433901726. The cubic root of 20987791 is about 275.8389410745.

It can be divided in two parts, 2098 and 7791, that added together give a palindrome (9889).

The spelling of 20987791 in words is "twenty million, nine hundred eighty-seven thousand, seven hundred ninety-one".