21291643 has 2 divisors, whose sum is σ = 21291644. Its totient is φ = 21291642.

The previous prime is 21291593. The next prime is 21291661. The reversal of 21291643 is 34619212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21291643 - 2¹⁷ = 21160571 is a prime.

It is not a weakly prime, because it can be changed into another prime (21291943) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10645821 + 10645822.

It is an arithmetic number, because the mean of its divisors is an integer number (10645822).

Almost surely, 2^21291643 is an apocalyptic number.

21291643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21291643 is an equidigital number, since it uses as much as digits as its factorization.

21291643 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2592, while the sum is 28.

The square root of 21291643 is about 4614.2868354709. The cubic root of 21291643 is about 277.1637265333.

The spelling of 21291643 in words is "twenty-one million, two hundred ninety-one thousand, six hundred forty-three".