21208212556 has 12 divisors (see below), whose sum is σ = 37143860040. Its totient is φ = 10595681120.

The previous prime is 21208212551. The next prime is 21208212563. The reversal of 21208212556 is 65521280212.

It is not an unprimeable number, because it can be changed into a prime (21208212551) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2100625 + ... + 2110696.

It is an arithmetic number, because the mean of its divisors is an integer number (3095321670).

Almost surely, 2^21208212556 is an apocalyptic number.

It is an amenable number.

21208212556 is a deficient number, since it is larger than the sum of its proper divisors (15935647484).

21208212556 is a wasteful number, since it uses less digits than its factorization.

21208212556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4212584 (or 4212582 counting only the distinct ones).

The product of its (nonzero) digits is 19200, while the sum is 34.

Adding to 21208212556 its reverse (65521280212), we get a palindrome (86729492768).

The spelling of 21208212556 in words is "twenty-one billion, two hundred eight million, two hundred twelve thousand, five hundred fifty-six".