2171721687 has 4 divisors (see below), whose sum is σ = 2895628920. Its totient is φ = 1447814456.

The previous prime is 2171721677. The next prime is 2171721733. The reversal of 2171721687 is 7861271712.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2171721687 is a prime.

It is a super-2 number, since 2×2171721687² = 9432750171572251938, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2171721677) 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, 361953612 + ... + 361953617.

It is an arithmetic number, because the mean of its divisors is an integer number (723907230).

Almost surely, 2^2171721687 is an apocalyptic number.

2171721687 is a deficient number, since it is larger than the sum of its proper divisors (723907233).

2171721687 is an equidigital number, since it uses as much as digits as its factorization.

2171721687 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 723907232.

The product of its digits is 65856, while the sum is 42.

The square root of 2171721687 is about 46601.7348067644. The cubic root of 2171721687 is about 1294.9948941128.

The spelling of 2171721687 in words is "two billion, one hundred seventy-one million, seven hundred twenty-one thousand, six hundred eighty-seven".