21291091 has 2 divisors, whose sum is σ = 21291092. Its totient is φ = 21291090.

The previous prime is 21291029. The next prime is 21291097. The reversal of 21291091 is 19019212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21291091 is a prime.

It is not a weakly prime, because it can be changed into another prime (21291097) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10645545 + 10645546.

It is an arithmetic number, because the mean of its divisors is an integer number (10645546).

Almost surely, 2^21291091 is an apocalyptic number.

21291091 is a deficient number, since it is larger than the sum of its proper divisors (1).

21291091 is an equidigital number, since it uses as much as digits as its factorization.

21291091 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324, while the sum is 25.

The square root of 21291091 is about 4614.2270208563. The cubic root of 21291091 is about 277.1613312946.

The spelling of 21291091 in words is "twenty-one million, two hundred ninety-one thousand, ninety-one".