21918286799809 has 3 divisors (see below), whose sum is σ = 21918291481507. Its totient is φ = 21918282118112.

The previous prime is 21918286799797. The next prime is 21918286799819. The reversal of 21918286799809 is 90899768281912.

The square root of 21918286799809 is 4681697.

It is a perfect power (a square), and thus also a powerful number.

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 can be written as a sum of positive squares in only one way, i.e., 13201195889025 + 8717090910784 = 3633345^2 + 2952472^2 .

It is not a de Polignac number, because 21918286799809 - 2¹⁹ = 21918286275521 is a prime.

It is a super-2 number, since 2×21918286799809² (a number of 27 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21918286799819) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 2340849 + ... + 7022545.

Almost surely, 2^{21918286799809} is an apocalyptic number.

21918286799809 is the 4681697-th square number.

21918286799809 is the 2340849-th centered octagonal number.

It is an amenable number.

21918286799809 is a deficient number, since it is larger than the sum of its proper divisors (4681698).

21918286799809 is an frugal number, since it uses more digits than its factorization.

21918286799809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9363394 (or 4681697 counting only the distinct ones).

The product of its (nonzero) digits is 564350976, while the sum is 79.

The spelling of 21918286799809 in words is "twenty-one trillion, nine hundred eighteen billion, two hundred eighty-six million, seven hundred ninety-nine thousand, eight hundred nine".