21000551 has 8 divisors (see below), whose sum is σ = 24672144. Its totient is φ = 17622720.

The previous prime is 21000533. The next prime is 21000557. The reversal of 21000551 is 15500012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21000551 - 2¹⁸ = 20738407 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000557) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 73286 + ... + 73571.

It is an arithmetic number, because the mean of its divisors is an integer number (3084018).

Almost surely, 2^21000551 is an apocalyptic number.

21000551 is a deficient number, since it is larger than the sum of its proper divisors (3671593).

21000551 is a wasteful number, since it uses less digits than its factorization.

21000551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 146881.

The product of its (nonzero) digits is 50, while the sum is 14.

The square root of 21000551 is about 4582.6358135903. The cubic root of 21000551 is about 275.8948305809.

Adding to 21000551 its reverse (15500012), we get a palindrome (36500563).

The spelling of 21000551 in words is "twenty-one million, five hundred fifty-one", and thus it is an aban number.