21086815369 has 3 divisors (see below), whose sum is σ = 21086960583. Its totient is φ = 21086670156.

The previous prime is 21086815361. The next prime is 21086815397. The reversal of 21086815369 is 96351868012.

The square root of 21086815369 is 145213.

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., 17700972025 + 3385843344 = 133045^2 + 58188^2 .

It is not a de Polignac number, because 21086815369 - 2³ = 21086815361 is a prime.

It is a super-2 number, since 2×21086815369² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21086815361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 72607 + ... + 217819.

It is an arithmetic number, because the mean of its divisors is an integer number (7028986861).

Almost surely, 2^21086815369 is an apocalyptic number.

21086815369 is the 145213-rd square number.

21086815369 is the 72607-th centered octagonal number.

It is an amenable number.

21086815369 is a deficient number, since it is larger than the sum of its proper divisors (145214).

21086815369 is an frugal number, since it uses more digits than its factorization.

21086815369 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 290426 (or 145213 counting only the distinct ones).

The product of its (nonzero) digits is 622080, while the sum is 49.

Multiplying 21086815369 by its sum of digits (49), we get a square (1033253953081 = 1016491²).

The spelling of 21086815369 in words is "twenty-one billion, eighty-six million, eight hundred fifteen thousand, three hundred sixty-nine".