21131897 has 2 divisors, whose sum is σ = 21131898. Its totient is φ = 21131896.

The previous prime is 21131881. The next prime is 21131899. The reversal of 21131897 is 79813112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17147881 + 3984016 = 4141^2 + 1996^2 .

It is a cyclic number.

It is not a de Polignac number, because 21131897 - 2⁴ = 21131881 is a prime.

Together with 21131899, 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 (21131899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10565948 + 10565949.

It is an arithmetic number, because the mean of its divisors is an integer number (10565949).

Almost surely, 2^21131897 is an apocalyptic number.

It is an amenable number.

21131897 is a deficient number, since it is larger than the sum of its proper divisors (1).

21131897 is an equidigital number, since it uses as much as digits as its factorization.

21131897 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3024, while the sum is 32.

The square root of 21131897 is about 4596.9443111702. The cubic root of 21131897 is about 276.4688217970.

The spelling of 21131897 in words is "twenty-one million, one hundred thirty-one thousand, eight hundred ninety-seven".