21665120242 has 4 divisors (see below), whose sum is σ = 32497680366. Its totient is φ = 10832560120.

The previous prime is 21665120221. The next prime is 21665120251. The reversal of 21665120242 is 24202156612.

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., 17463358201 + 4201762041 = 132149^2 + 64821^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5416280059 + ... + 5416280062.

Almost surely, 2^21665120242 is an apocalyptic number.

21665120242 is a deficient number, since it is larger than the sum of its proper divisors (10832560124).

21665120242 is a wasteful number, since it uses less digits than its factorization.

21665120242 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10832560123.

The product of its (nonzero) digits is 11520, while the sum is 31.

Adding to 21665120242 its reverse (24202156612), we get a palindrome (45867276854).

The spelling of 21665120242 in words is "twenty-one billion, six hundred sixty-five million, one hundred twenty thousand, two hundred forty-two".