21186981 has 32 divisors (see below), whose sum is σ = 34329600. Its totient is φ = 12856320.

The previous prime is 21186967. The next prime is 21186983. The reversal of 21186981 is 18968112.

It is not a de Polignac number, because 21186981 - 2⁹ = 21186469 is a prime.

It is a super-2 number, since 2×21186981² = 897776327788722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21186983) 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 31 ways as a sum of consecutive naturals, for example, 13485 + ... + 14973.

It is an arithmetic number, because the mean of its divisors is an integer number (1072800).

Almost surely, 2^21186981 is an apocalyptic number.

It is an amenable number.

21186981 is a deficient number, since it is larger than the sum of its proper divisors (13142619).

21186981 is a wasteful number, since it uses less digits than its factorization.

21186981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1546 (or 1540 counting only the distinct ones).

The product of its digits is 6912, while the sum is 36.

The square root of 21186981 is about 4602.9317831139. The cubic root of 21186981 is about 276.7088348816.

The spelling of 21186981 in words is "twenty-one million, one hundred eighty-six thousand, nine hundred eighty-one".