21005451 has 6 divisors (see below), whose sum is σ = 30341220. Its totient is φ = 14003628.

The previous prime is 21005441. The next prime is 21005473. The reversal of 21005451 is 15450012.

21005451 is a `hidden beast` number, since 210 + 0 + 5 + 451 = 666.

It is not a de Polignac number, because 21005451 - 2¹⁷ = 20874379 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21005401) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1166961 + ... + 1166978.

It is an arithmetic number, because the mean of its divisors is an integer number (5056870).

Almost surely, 2^21005451 is an apocalyptic number.

21005451 is a deficient number, since it is larger than the sum of its proper divisors (9335769).

21005451 is a wasteful number, since it uses less digits than its factorization.

21005451 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2333945 (or 2333942 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21005451 is about 4583.1704092255. The cubic root of 21005451 is about 275.9162868360.

Adding to 21005451 its reverse (15450012), we get a palindrome (36455463).

The spelling of 21005451 in words is "twenty-one million, five thousand, four hundred fifty-one".