20991536 has 10 divisors (see below), whose sum is σ = 40671132. Its totient is φ = 10495760.

The previous prime is 20991533. The next prime is 20991577. The reversal of 20991536 is 63519902.

It is a junction number, because it is equal to n+sod(n) for n = 20991496 and 20991505.

It is not an unprimeable number, because it can be changed into a prime (20991533) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 655970 + ... + 656001.

Almost surely, 2^20991536 is an apocalyptic number.

It is an amenable number.

20991536 is a deficient number, since it is larger than the sum of its proper divisors (19679596).

20991536 is a wasteful number, since it uses less digits than its factorization.

20991536 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1311979 (or 1311973 counting only the distinct ones).

The product of its (nonzero) digits is 14580, while the sum is 35.

The square root of 20991536 is about 4581.6521037722. The cubic root of 20991536 is about 275.8553467299.

The spelling of 20991536 in words is "twenty million, nine hundred ninety-one thousand, five hundred thirty-six".