21111506665 has 8 divisors (see below), whose sum is σ = 25340833800. Its totient is φ = 16884521472.

The previous prime is 21111506659. The next prime is 21111506683. The reversal of 21111506665 is 56660511112.

It can be written as a sum of positive squares in 4 ways, for example, as 735657129 + 20375849536 = 27123^2 + 142744^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21111506665 - 2²¹ = 21109409513 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21111506665.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 565590 + ... + 601759.

It is an arithmetic number, because the mean of its divisors is an integer number (3167604225).

Almost surely, 2^21111506665 is an apocalyptic number.

It is an amenable number.

21111506665 is a deficient number, since it is larger than the sum of its proper divisors (4229327135).

21111506665 is a wasteful number, since it uses less digits than its factorization.

21111506665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1170971.

The product of its (nonzero) digits is 10800, while the sum is 34.

The spelling of 21111506665 in words is "twenty-one billion, one hundred eleven million, five hundred six thousand, six hundred sixty-five".