21644243236 has 48 divisors (see below), whose sum is σ = 47236976640. Its totient is φ = 8430469920.

The previous prime is 21644243233. The next prime is 21644243237. The reversal of 21644243236 is 63234244612.

It is a junction number, because it is equal to n+sod(n) for n = 21644243195 and 21644243204.

It is not an unprimeable number, because it can be changed into a prime (21644243233) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1447245 + ... + 1462123.

It is an arithmetic number, because the mean of its divisors is an integer number (984103680).

Almost surely, 2^21644243236 is an apocalyptic number.

It is an amenable number.

21644243236 is an abundant number, since it is smaller than the sum of its proper divisors (25592733404).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21644243236 is a wasteful number, since it uses less digits than its factorization.

21644243236 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19624 (or 19622 counting only the distinct ones).

The product of its digits is 165888, while the sum is 37.

Adding to 21644243236 its reverse (63234244612), we get a palindrome (84878487848).

The spelling of 21644243236 in words is "twenty-one billion, six hundred forty-four million, two hundred forty-three thousand, two hundred thirty-six".