21001021205 has 8 divisors (see below), whose sum is σ = 26070233400. Its totient is φ = 16221478336.

The previous prime is 21001021187. The next prime is 21001021219. The reversal of 21001021205 is 50212010012.

It can be written as a sum of positive squares in 4 ways, for example, as 2198578321 + 18802442884 = 46889^2 + 137122^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21001021205 - 2⁸ = 21001020949 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21001021205.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 72417170 + ... + 72417459.

It is an arithmetic number, because the mean of its divisors is an integer number (3258779175).

Almost surely, 2^21001021205 is an apocalyptic number.

It is an amenable number.

21001021205 is a deficient number, since it is larger than the sum of its proper divisors (5069212195).

21001021205 is a wasteful number, since it uses less digits than its factorization.

21001021205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 144834663.

The product of its (nonzero) digits is 40, while the sum is 14.

Adding to 21001021205 its reverse (50212010012), we get a palindrome (71213031217).

The spelling of 21001021205 in words is "twenty-one billion, one million, twenty-one thousand, two hundred five".