21506021671 has 4 divisors (see below), whose sum is σ = 21535604272. Its totient is φ = 21476439072.

The previous prime is 21506021627. The next prime is 21506021687. The reversal of 21506021671 is 17612060512.

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

It is a cyclic number.

It is not a de Polignac number, because 21506021671 - 2⁷ = 21506021543 is a prime.

It is a super-3 number, since 3×21506021671³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506021171) 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, 14790210 + ... + 14791663.

It is an arithmetic number, because the mean of its divisors is an integer number (5383901068).

Almost surely, 2^21506021671 is an apocalyptic number.

21506021671 is a deficient number, since it is larger than the sum of its proper divisors (29582601).

21506021671 is an equidigital number, since it uses as much as digits as its factorization.

21506021671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29582600.

The product of its (nonzero) digits is 5040, while the sum is 31.

The spelling of 21506021671 in words is "twenty-one billion, five hundred six million, twenty-one thousand, six hundred seventy-one".