21801217549 has 4 divisors (see below), whose sum is σ = 22158614620. Its totient is φ = 21443820480.

The previous prime is 21801217523. The next prime is 21801217553. The reversal of 21801217549 is 94571210812.

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

It can be written as a sum of positive squares in 2 ways, for example, as 406304649 + 21394912900 = 20157^2 + 146270^2 .

It is a cyclic number.

It is not a de Polignac number, because 21801217549 - 2²¹ = 21799120397 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 (21801217049) 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, 178698444 + ... + 178698565.

It is an arithmetic number, because the mean of its divisors is an integer number (5539653655).

Almost surely, 2^21801217549 is an apocalyptic number.

It is an amenable number.

21801217549 is a deficient number, since it is larger than the sum of its proper divisors (357397071).

21801217549 is an equidigital number, since it uses as much as digits as its factorization.

21801217549 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 357397070.

The product of its (nonzero) digits is 40320, while the sum is 40.

The spelling of 21801217549 in words is "twenty-one billion, eight hundred one million, two hundred seventeen thousand, five hundred forty-nine".