21501791 has 4 divisors (see below), whose sum is σ = 21512400. Its totient is φ = 21491184.

The previous prime is 21501737. The next prime is 21501811. The reversal of 21501791 is 19710512.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21501791 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21501791.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21501721) 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, 1211 + ... + 6668.

It is an arithmetic number, because the mean of its divisors is an integer number (5378100).

Almost surely, 2^21501791 is an apocalyptic number.

21501791 is a deficient number, since it is larger than the sum of its proper divisors (10609).

21501791 is an equidigital number, since it uses as much as digits as its factorization.

21501791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10608.

The product of its (nonzero) digits is 630, while the sum is 26.

The square root of 21501791 is about 4637.0023722228. The cubic root of 21501791 is about 278.0726092623.

The spelling of 21501791 in words is "twenty-one million, five hundred one thousand, seven hundred ninety-one".