21766649 has 2 divisors, whose sum is σ = 21766650. Its totient is φ = 21766648.

The previous prime is 21766621. The next prime is 21766651. The reversal of 21766649 is 94666712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18003049 + 3763600 = 4243^2 + 1940^2 .

It is a cyclic number.

It is not a de Polignac number, because 21766649 - 2²⁰ = 20718073 is a prime.

Together with 21766651, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21766049) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10883324 + 10883325.

It is an arithmetic number, because the mean of its divisors is an integer number (10883325).

Almost surely, 2^21766649 is an apocalyptic number.

It is an amenable number.

21766649 is a deficient number, since it is larger than the sum of its proper divisors (1).

21766649 is an equidigital number, since it uses as much as digits as its factorization.

21766649 is an evil number, because the sum of its binary digits is even.

The product of its digits is 108864, while the sum is 41.

The square root of 21766649 is about 4665.4741452504. The cubic root of 21766649 is about 279.2097145863.

It can be divided in two parts, 217 and 66649, that added together give a palindrome (66866).

The spelling of 21766649 in words is "twenty-one million, seven hundred sixty-six thousand, six hundred forty-nine".