21663643426 has 4 divisors (see below), whose sum is σ = 32495465142. Its totient is φ = 10831821712.

The previous prime is 21663643381. The next prime is 21663643453. The reversal of 21663643426 is 62434636612.

It is a happy number.

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., 13971476401 + 7692167025 = 118201^2 + 87705^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5415910855 + ... + 5415910858.

Almost surely, 2^21663643426 is an apocalyptic number.

21663643426 is a deficient number, since it is larger than the sum of its proper divisors (10831821716).

21663643426 is a wasteful number, since it uses less digits than its factorization.

21663643426 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10831821715.

The product of its digits is 746496, while the sum is 43.

It can be divided in two parts, 216636 and 43426, that added together give a palindrome (260062).

The spelling of 21663643426 in words is "twenty-one billion, six hundred sixty-three million, six hundred forty-three thousand, four hundred twenty-six".