21390657826 has 4 divisors (see below), whose sum is σ = 32085986742. Its totient is φ = 10695328912.

The previous prime is 21390657811. The next prime is 21390657829. The reversal of 21390657826 is 62875609312.

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

It can be written as a sum of positive squares in only one way, i.e., 21343749025 + 46908801 = 146095^2 + 6849^2 .

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21390657826.

It is not an unprimeable number, because it can be changed into a prime (21390657829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5347664455 + ... + 5347664458.

Almost surely, 2^21390657826 is an apocalyptic number.

21390657826 is a deficient number, since it is larger than the sum of its proper divisors (10695328916).

21390657826 is a wasteful number, since it uses less digits than its factorization.

21390657826 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10695328915.

The product of its (nonzero) digits is 1088640, while the sum is 49.

The spelling of 21390657826 in words is "twenty-one billion, three hundred ninety million, six hundred fifty-seven thousand, eight hundred twenty-six".