21988387 has 2 divisors, whose sum is σ = 21988388. Its totient is φ = 21988386.

The previous prime is 21988367. The next prime is 21988411. The reversal of 21988387 is 78388912.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21988387 is a prime.

It is not a weakly prime, because it can be changed into another prime (21988367) 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 as a sum of consecutive naturals, namely, 10994193 + 10994194.

It is an arithmetic number, because the mean of its divisors is an integer number (10994194).

Almost surely, 2^21988387 is an apocalyptic number.

21988387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21988387 is an equidigital number, since it uses as much as digits as its factorization.

21988387 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 193536, while the sum is 46.

The square root of 21988387 is about 4689.1776464536. The cubic root of 21988387 is about 280.1546212322.

It can be divided in two parts, 2198 and 8387, that added together give a triangular number (10585 = T₁₄₅).

The spelling of 21988387 in words is "twenty-one million, nine hundred eighty-eight thousand, three hundred eighty-seven".