21156106605217 has 4 divisors (see below), whose sum is σ = 21173045042500. Its totient is φ = 21139168167936.

The previous prime is 21156106605169. The next prime is 21156106605223. The reversal of 21156106605217 is 71250660165112.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 14175947889216 + 6980158716001 = 3765096^2 + 2641999^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21156106605217 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21156106605017) 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, 8469216768 + ... + 8469219265.

It is an arithmetic number, because the mean of its divisors is an integer number (5293261260625).

Almost surely, 2^{21156106605217} is an apocalyptic number.

It is an amenable number.

21156106605217 is a deficient number, since it is larger than the sum of its proper divisors (16938437283).

21156106605217 is a wasteful number, since it uses less digits than its factorization.

21156106605217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16938437282.

The product of its (nonzero) digits is 151200, while the sum is 43.

The spelling of 21156106605217 in words is "twenty-one trillion, one hundred fifty-six billion, one hundred six million, six hundred five thousand, two hundred seventeen".