21506212165601 has 16 divisors (see below), whose sum is σ = 21919520246400. Its totient is φ = 21096767797248.

The previous prime is 21506212165597. The next prime is 21506212165621. The reversal of 21506212165601 is 10656121260512.

It is a cyclic number.

It is not a de Polignac number, because 21506212165601 - 2² = 21506212165597 is a prime.

It is a super-4 number, since 4×21506212165601⁴ (a number of 54 digits) contains 4444 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21506212165621) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17775020 + ... + 18946338.

It is an arithmetic number, because the mean of its divisors is an integer number (1369970015400).

Almost surely, 2^{21506212165601} is an apocalyptic number.

It is an amenable number.

21506212165601 is a deficient number, since it is larger than the sum of its proper divisors (413308080799).

21506212165601 is a wasteful number, since it uses less digits than its factorization.

21506212165601 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1172968.

The product of its (nonzero) digits is 43200, while the sum is 38.

The spelling of 21506212165601 in words is "twenty-one trillion, five hundred six billion, two hundred twelve million, one hundred sixty-five thousand, six hundred one".