21391129 has 2 divisors, whose sum is σ = 21391130. Its totient is φ = 21391128.

The previous prime is 21391091. The next prime is 21391133. The reversal of 21391129 is 92119312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20793600 + 597529 = 4560^2 + 773^2 .

It is a cyclic number.

It is not a de Polignac number, because 21391129 - 2⁹ = 21390617 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21391097 and 21391106.

It is not a weakly prime, because it can be changed into another prime (21391189) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10695564 + 10695565.

It is an arithmetic number, because the mean of its divisors is an integer number (10695565).

Almost surely, 2^21391129 is an apocalyptic number.

It is an amenable number.

21391129 is a deficient number, since it is larger than the sum of its proper divisors (1).

21391129 is an equidigital number, since it uses as much as digits as its factorization.

21391129 is an evil number, because the sum of its binary digits is even.

The product of its digits is 972, while the sum is 28.

The square root of 21391129 is about 4625.0544861655. The cubic root of 21391129 is about 277.5947418840.

The spelling of 21391129 in words is "twenty-one million, three hundred ninety-one thousand, one hundred twenty-nine".