21766981 has 2 divisors, whose sum is σ = 21766982. Its totient is φ = 21766980.

The previous prime is 21766961. The next prime is 21767029. The reversal of 21766981 is 18966712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17564481 + 4202500 = 4191^2 + 2050^2 .

It is a cyclic number.

It is not a de Polignac number, because 21766981 - 2⁷ = 21766853 is a prime.

It is a super-2 number, since 2×21766981² = 947602923708722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21766931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10883490 + 10883491.

It is an arithmetic number, because the mean of its divisors is an integer number (10883491).

Almost surely, 2^21766981 is an apocalyptic number.

It is an amenable number.

21766981 is a deficient number, since it is larger than the sum of its proper divisors (1).

21766981 is an equidigital number, since it uses as much as digits as its factorization.

21766981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 40.

The square root of 21766981 is about 4665.5097256356. The cubic root of 21766981 is about 279.2111341457.

The spelling of 21766981 in words is "twenty-one million, seven hundred sixty-six thousand, nine hundred eighty-one".