20281991 has 4 divisors (see below), whose sum is σ = 20981400. Its totient is φ = 19582584.

The previous prime is 20281973. The next prime is 20281993. The reversal of 20281991 is 19918202.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20281991 is a prime.

It is a super-2 number, since 2×20281991² = 822718317848162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20281993) 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, 349661 + ... + 349718.

It is an arithmetic number, because the mean of its divisors is an integer number (5245350).

Almost surely, 2^20281991 is an apocalyptic number.

20281991 is a deficient number, since it is larger than the sum of its proper divisors (699409).

20281991 is an equidigital number, since it uses as much as digits as its factorization.

20281991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 699408.

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 20281991 is about 4503.5531527895. The cubic root of 20281991 is about 272.7115479856.

The spelling of 20281991 in words is "twenty million, two hundred eighty-one thousand, nine hundred ninety-one".