21764381 has 2 divisors, whose sum is σ = 21764382. Its totient is φ = 21764380.

The previous prime is 21764341. The next prime is 21764383. The reversal of 21764381 is 18346712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21576025 + 188356 = 4645^2 + 434^2 .

It is a cyclic number.

It is not a de Polignac number, because 21764381 - 2¹⁴ = 21747997 is a prime.

It is a super-2 number, since 2×21764381² = 947376560626322, which contains 22 as substring.

Together with 21764383, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21764383) 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 as a sum of consecutive naturals, namely, 10882190 + 10882191.

It is an arithmetic number, because the mean of its divisors is an integer number (10882191).

Almost surely, 2^21764381 is an apocalyptic number.

It is an amenable number.

21764381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21764381 is an equidigital number, since it uses as much as digits as its factorization.

21764381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 32.

The square root of 21764381 is about 4665.2310768064. The cubic root of 21764381 is about 279.2000167281.

The spelling of 21764381 in words is "twenty-one million, seven hundred sixty-four thousand, three hundred eighty-one".