21601265666 has 4 divisors (see below), whose sum is σ = 32401898502. Its totient is φ = 10800632832.

The previous prime is 21601265663. The next prime is 21601265669. The reversal of 21601265666 is 66656210612.

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

It is an interprime number because it is at equal distance from previous prime (21601265663) and next prime (21601265669).

It can be written as a sum of positive squares in only one way, i.e., 20670100441 + 931165225 = 143771^2 + 30515^2 .

It is a super-2 number, since 2×21601265666² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21601265663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5400316415 + ... + 5400316418.

Almost surely, 2^21601265666 is an apocalyptic number.

21601265666 is a deficient number, since it is larger than the sum of its proper divisors (10800632836).

21601265666 is a wasteful number, since it uses less digits than its factorization.

21601265666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10800632835.

The product of its (nonzero) digits is 155520, while the sum is 41.

The spelling of 21601265666 in words is "twenty-one billion, six hundred one million, two hundred sixty-five thousand, six hundred sixty-six".