21000051 has 12 divisors (see below), whose sum is σ = 31312320. Its totient is φ = 13548240.

The previous prime is 21000041. The next prime is 21000059. The reversal of 21000051 is 15000012.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-21000051 is a prime.

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

It is a junction number, because it is equal to n+sod(n) for n = 20999997 and 21000042.

It is not an unprimeable number, because it can be changed into a prime (21000059) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 37356 + ... + 37913.

It is an arithmetic number, because the mean of its divisors is an integer number (2609360).

Almost surely, 2^21000051 is an apocalyptic number.

21000051 is a deficient number, since it is larger than the sum of its proper divisors (10312269).

21000051 is a wasteful number, since it uses less digits than its factorization.

21000051 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 75306 (or 75303 counting only the distinct ones).

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

The square root of 21000051 is about 4582.5812595087. The cubic root of 21000051 is about 275.8926409794.

Adding to 21000051 its reverse (15000012), we get a palindrome (36000063).

The spelling of 21000051 in words is "twenty-one million, fifty-one", and thus it is an aban number and an uban number.