21381929 has 2 divisors, whose sum is σ = 21381930. Its totient is φ = 21381928.

The previous prime is 21381901. The next prime is 21381931. The reversal of 21381929 is 92918312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20475625 + 906304 = 4525^2 + 952^2 .

It is a cyclic number.

It is not a de Polignac number, because 21381929 - 2²⁰ = 20333353 is a prime.

It is a super-2 number, since 2×21381929² = 914373775522082, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 21381931, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21381979) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690964 + 10690965.

It is an arithmetic number, because the mean of its divisors is an integer number (10690965).

Almost surely, 2^21381929 is an apocalyptic number.

It is an amenable number.

21381929 is a deficient number, since it is larger than the sum of its proper divisors (1).

21381929 is an equidigital number, since it uses as much as digits as its factorization.

21381929 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7776, while the sum is 35.

The square root of 21381929 is about 4624.0597963262. The cubic root of 21381929 is about 277.5549397486.

The spelling of 21381929 in words is "twenty-one million, three hundred eighty-one thousand, nine hundred twenty-nine".