21001000005 has 20 divisors (see below), whose sum is σ = 37646237772. Its totient is φ = 11200533120.

The previous prime is 21001000001. The next prime is 21001000019. The reversal of 21001000005 is 50000010012.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 9379728801 + 11621271204 = 96849^2 + 107802^2 .

It is not a de Polignac number, because 21001000005 - 2² = 21001000001 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001000001) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 25926756 + ... + 25927565.

Almost surely, 2^21001000005 is an apocalyptic number.

It is an amenable number.

21001000005 is a deficient number, since it is larger than the sum of its proper divisors (16645237767).

21001000005 is an equidigital number, since it uses as much as digits as its factorization.

21001000005 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51854338 (or 51854329 counting only the distinct ones).

The product of its (nonzero) digits is 10, while the sum is 9.

Adding to 21001000005 its reverse (50000010012), we get a palindrome (71001010017).

The spelling of 21001000005 in words is "twenty-one billion, one million, five", and thus it is an aban number and an uban number.