21138569761 has 4 divisors (see below), whose sum is σ = 21143794500. Its totient is φ = 21133345024.

The previous prime is 21138569723. The next prime is 21138569779. The reversal of 21138569761 is 16796583112.

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

It can be written as a sum of positive squares in 2 ways, for example, as 10252777536 + 10885792225 = 101256^2 + 104335^2 .

It is a cyclic number.

It is not a de Polignac number, because 21138569761 - 2¹¹ = 21138567713 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21138569461) 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, 2606296 + ... + 2614393.

It is an arithmetic number, because the mean of its divisors is an integer number (5285948625).

Almost surely, 2^21138569761 is an apocalyptic number.

It is an amenable number.

21138569761 is a deficient number, since it is larger than the sum of its proper divisors (5224739).

21138569761 is an equidigital number, since it uses as much as digits as its factorization.

21138569761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5224738.

The product of its digits is 544320, while the sum is 49.

The spelling of 21138569761 in words is "twenty-one billion, one hundred thirty-eight million, five hundred sixty-nine thousand, seven hundred sixty-one".