21306625406666 has 4 divisors (see below), whose sum is σ = 31959938110002. Its totient is φ = 10653312703332.

The previous prime is 21306625406657. The next prime is 21306625406669. The reversal of 21306625406666 is 66660452660312.

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

It can be written as a sum of positive squares in only one way, i.e., 20028945587641 + 1277679819025 = 4475371^2 + 1130345^2 .

It is not an unprimeable number, because it can be changed into a prime (21306625406669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5326656351665 + ... + 5326656351668.

Almost surely, 2^{21306625406666} is an apocalyptic number.

21306625406666 is a deficient number, since it is larger than the sum of its proper divisors (10653312703336).

21306625406666 is a wasteful number, since it uses less digits than its factorization.

21306625406666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10653312703335.

The product of its (nonzero) digits is 11197440, while the sum is 53.

The spelling of 21306625406666 in words is "twenty-one trillion, three hundred six billion, six hundred twenty-five million, four hundred six thousand, six hundred sixty-six".