21705299217 has 128 divisors (see below), whose sum is σ = 38239027200. Its totient is φ = 12063841920.

The previous prime is 21705299149. The next prime is 21705299267. The reversal of 21705299217 is 71299250712.

21705299217 is a `hidden beast` number, since 21 + 7 + 0 + 529 + 92 + 17 = 666.

It is not a de Polignac number, because 21705299217 - 2¹¹ = 21705297169 is a prime.

It is a super-2 number, since 2×21705299217² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21705299267) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 158432773 + ... + 158432909.

It is an arithmetic number, because the mean of its divisors is an integer number (298742400).

Almost surely, 2^21705299217 is an apocalyptic number.

21705299217 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21705299217 is a deficient number, since it is larger than the sum of its proper divisors (16533727983).

21705299217 is an equidigital number, since it uses as much as digits as its factorization.

21705299217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 375 (or 357 counting only the distinct ones).

The product of its (nonzero) digits is 158760, while the sum is 45.

The spelling of 21705299217 in words is "twenty-one billion, seven hundred five million, two hundred ninety-nine thousand, two hundred seventeen".