21721406205 has 16 divisors (see below), whose sum is σ = 34928899200. Its totient is φ = 11526533568.

The previous prime is 21721406197. The next prime is 21721406219. The reversal of 21721406205 is 50260412712.

It is not a de Polignac number, because 21721406205 - 2³ = 21721406197 is a prime.

It is a super-2 number, since 2×21721406205² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3635442 + ... + 3641411.

It is an arithmetic number, because the mean of its divisors is an integer number (2183056200).

Almost surely, 2^21721406205 is an apocalyptic number.

It is an amenable number.

21721406205 is a deficient number, since it is larger than the sum of its proper divisors (13207492995).

21721406205 is a wasteful number, since it uses less digits than its factorization.

21721406205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7277060.

The product of its (nonzero) digits is 6720, while the sum is 30.

Adding to 21721406205 its reverse (50260412712), we get a palindrome (71981818917).

The spelling of 21721406205 in words is "twenty-one billion, seven hundred twenty-one million, four hundred six thousand, two hundred five".