21855487 has 2 divisors, whose sum is σ = 21855488. Its totient is φ = 21855486.

The previous prime is 21855439. The next prime is 21855503. The reversal of 21855487 is 78455812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21855487 - 2¹⁵ = 21822719 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21855437) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10927743 + 10927744.

It is an arithmetic number, because the mean of its divisors is an integer number (10927744).

Almost surely, 2^21855487 is an apocalyptic number.

21855487 is a deficient number, since it is larger than the sum of its proper divisors (1).

21855487 is an equidigital number, since it uses as much as digits as its factorization.

21855487 is an evil number, because the sum of its binary digits is even.

The product of its digits is 89600, while the sum is 40.

The square root of 21855487 is about 4674.9852406184. The cubic root of 21855487 is about 279.5890527729.

The spelling of 21855487 in words is "twenty-one million, eight hundred fifty-five thousand, four hundred eighty-seven".