21661002165 has 32 divisors (see below), whose sum is σ = 38026889856. Its totient is φ = 10441583360.

The previous prime is 21661002137. The next prime is 21661002199. The reversal of 21661002165 is 56120016612.

It is not a de Polignac number, because 21661002165 - 2⁵ = 21661002133 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 350874 + ... + 407963.

It is an arithmetic number, because the mean of its divisors is an integer number (1188340308).

Almost surely, 2^21661002165 is an apocalyptic number.

It is an amenable number.

21661002165 is a deficient number, since it is larger than the sum of its proper divisors (16365887691).

21661002165 is a wasteful number, since it uses less digits than its factorization.

21661002165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 759029.

The product of its (nonzero) digits is 4320, while the sum is 30.

Adding to 21661002165 its reverse (56120016612), we get a palindrome (77781018777).

The spelling of 21661002165 in words is "twenty-one billion, six hundred sixty-one million, two thousand, one hundred sixty-five".