21987547 has 2 divisors, whose sum is σ = 21987548. Its totient is φ = 21987546.

The previous prime is 21987533. The next prime is 21987557. The reversal of 21987547 is 74578912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21987547 - 2¹¹ = 21985499 is a prime.

It is not a weakly prime, because it can be changed into another prime (21987557) 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 as a sum of consecutive naturals, namely, 10993773 + 10993774.

It is an arithmetic number, because the mean of its divisors is an integer number (10993774).

Almost surely, 2^21987547 is an apocalyptic number.

21987547 is a deficient number, since it is larger than the sum of its proper divisors (1).

21987547 is an equidigital number, since it uses as much as digits as its factorization.

21987547 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 141120, while the sum is 43.

The square root of 21987547 is about 4689.0880776543. The cubic root of 21987547 is about 280.1510536994.

The spelling of 21987547 in words is "twenty-one million, nine hundred eighty-seven thousand, five hundred forty-seven".