21913121 has 2 divisors, whose sum is σ = 21913122. Its totient is φ = 21913120.

The previous prime is 21913117. The next prime is 21913123. The reversal of 21913121 is 12131912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19678096 + 2235025 = 4436^2 + 1495^2 .

It is a cyclic number.

It is not a de Polignac number, because 21913121 - 2² = 21913117 is a prime.

Together with 21913123, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21913093 and 21913102.

It is not a weakly prime, because it can be changed into another prime (21913123) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10956560 + 10956561.

It is an arithmetic number, because the mean of its divisors is an integer number (10956561).

Almost surely, 2^21913121 is an apocalyptic number.

It is an amenable number.

21913121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21913121 is an equidigital number, since it uses as much as digits as its factorization.

21913121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 108, while the sum is 20.

The square root of 21913121 is about 4681.1452658511. The cubic root of 21913121 is about 279.8346004449.

The spelling of 21913121 in words is "twenty-one million, nine hundred thirteen thousand, one hundred twenty-one".