21086981 has 2 divisors, whose sum is σ = 21086982. Its totient is φ = 21086980.

The previous prime is 21086971. The next prime is 21087019. The reversal of 21086981 is 18968012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20784481 + 302500 = 4559^2 + 550^2 .

It is a cyclic number.

It is not a de Polignac number, because 21086981 - 2²² = 16892677 is a prime.

It is a super-2 number, since 2×21086981² = 889321535388722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21086911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10543490 + 10543491.

It is an arithmetic number, because the mean of its divisors is an integer number (10543491).

Almost surely, 2^21086981 is an apocalyptic number.

It is an amenable number.

21086981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21086981 is an equidigital number, since it uses as much as digits as its factorization.

21086981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6912, while the sum is 35.

The square root of 21086981 is about 4592.0562932090. The cubic root of 21086981 is about 276.2728040251.

The spelling of 21086981 in words is "twenty-one million, eighty-six thousand, nine hundred eighty-one".