21766381 has 16 divisors (see below), whose sum is σ = 28201600. Its totient is φ = 16314048.

The previous prime is 21766373. The next prime is 21766391. The reversal of 21766381 is 18366712.

It is a cyclic number.

It is not a de Polignac number, because 21766381 - 2³ = 21766373 is a prime.

It is a super-2 number, since 2×21766381² = 947550683674322, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21766301) 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 15 ways as a sum of consecutive naturals, for example, 4566 + ... + 8023.

It is an arithmetic number, because the mean of its divisors is an integer number (1762600).

Almost surely, 2^21766381 is an apocalyptic number.

It is an amenable number.

21766381 is a deficient number, since it is larger than the sum of its proper divisors (6435219).

21766381 is a wasteful number, since it uses less digits than its factorization.

21766381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12628.

The product of its digits is 12096, while the sum is 34.

The square root of 21766381 is about 4665.4454235367. The cubic root of 21766381 is about 279.2085686664.

The spelling of 21766381 in words is "twenty-one million, seven hundred sixty-six thousand, three hundred eighty-one".