21718520191 has 4 divisors (see below), whose sum is σ = 21719672712. Its totient is φ = 21717367672.

The previous prime is 21718520137. The next prime is 21718520203. The reversal of 21718520191 is 19102581712.

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-21718520191 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 21718520191.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21718560191) 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, 547516 + ... + 585841.

It is an arithmetic number, because the mean of its divisors is an integer number (5429918178).

Almost surely, 2^21718520191 is an apocalyptic number.

21718520191 is a deficient number, since it is larger than the sum of its proper divisors (1152521).

21718520191 is a wasteful number, since it uses less digits than its factorization.

21718520191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1152520.

The product of its (nonzero) digits is 10080, while the sum is 37.

The spelling of 21718520191 in words is "twenty-one billion, seven hundred eighteen million, five hundred twenty thousand, one hundred ninety-one".