21047551 has 4 divisors (see below), whose sum is σ = 24054352. Its totient is φ = 18040752.

The previous prime is 21047539. The next prime is 21047563. The reversal of 21047551 is 15574012.

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

It is an interprime number because it is at equal distance from previous prime (21047539) and next prime (21047563).

It is a cyclic number.

It is not a de Polignac number, because 21047551 - 2⁷ = 21047423 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21047531) 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 3 ways as a sum of consecutive naturals, for example, 1503390 + ... + 1503403.

It is an arithmetic number, because the mean of its divisors is an integer number (6013588).

Almost surely, 2^21047551 is an apocalyptic number.

21047551 is a deficient number, since it is larger than the sum of its proper divisors (3006801).

21047551 is an equidigital number, since it uses as much as digits as its factorization.

21047551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3006800.

The product of its (nonzero) digits is 1400, while the sum is 25.

The square root of 21047551 is about 4587.7610007497. The cubic root of 21047551 is about 276.1004981284.

The spelling of 21047551 in words is "twenty-one million, forty-seven thousand, five hundred fifty-one".