21543551 has 2 divisors, whose sum is σ = 21543552. Its totient is φ = 21543550.

The previous prime is 21543527. The next prime is 21543569. The reversal of 21543551 is 15534512.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21543551 is a prime.

It is a Chen prime.

It is equal to p_1362149 and since 21543551 and 1362149 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21543551.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21543451) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10771775 + 10771776.

It is an arithmetic number, because the mean of its divisors is an integer number (10771776).

Almost surely, 2^21543551 is an apocalyptic number.

21543551 is a deficient number, since it is larger than the sum of its proper divisors (1).

21543551 is an equidigital number, since it uses as much as digits as its factorization.

21543551 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3000, while the sum is 26.

The square root of 21543551 is about 4641.5030970581. The cubic root of 21543551 is about 278.2525136959.

The spelling of 21543551 in words is "twenty-one million, five hundred forty-three thousand, five hundred fifty-one".