21000047 has 4 divisors (see below), whose sum is σ = 21356040. Its totient is φ = 20644056.

The previous prime is 21000041. The next prime is 21000059. The reversal of 21000047 is 74000012.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21000047 - 2⁸ = 20999791 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20999995 and 21000040.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000041) 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, 177908 + ... + 178025.

It is an arithmetic number, because the mean of its divisors is an integer number (5339010).

Almost surely, 2^21000047 is an apocalyptic number.

21000047 is a deficient number, since it is larger than the sum of its proper divisors (355993).

21000047 is an equidigital number, since it uses as much as digits as its factorization.

21000047 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 355992.

The product of its (nonzero) digits is 56, while the sum is 14.

The square root of 21000047 is about 4582.5808230734. The cubic root of 21000047 is about 275.8926234625.

Adding to 21000047 its reverse (74000012), we get a palindrome (95000059).

The spelling of 21000047 in words is "twenty-one million, forty-seven", and thus it is an aban number and an uban number.