21661251540163 has 4 divisors (see below), whose sum is σ = 21664043306080. Its totient is φ = 21658459774248.

The previous prime is 21661251540101. The next prime is 21661251540199. The reversal of 21661251540163 is 36104515216612.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21661251540163 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661251540563) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1395871320 + ... + 1395886837.

It is an arithmetic number, because the mean of its divisors is an integer number (5416010826520).

Almost surely, 2^{21661251540163} is an apocalyptic number.

21661251540163 is a deficient number, since it is larger than the sum of its proper divisors (2791765917).

21661251540163 is an equidigital number, since it uses as much as digits as its factorization.

21661251540163 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2791765916.

The product of its (nonzero) digits is 259200, while the sum is 43.

Adding to 21661251540163 its reverse (36104515216612), we get a palindrome (57765766756775).

The spelling of 21661251540163 in words is "twenty-one trillion, six hundred sixty-one billion, two hundred fifty-one million, five hundred forty thousand, one hundred sixty-three".