21172691 has 2 divisors, whose sum is σ = 21172692. Its totient is φ = 21172690.

The previous prime is 21172663. The next prime is 21172693. The reversal of 21172691 is 19627112.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21172691 - 2¹⁴ = 21156307 is a prime.

Together with 21172693, 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 (21172693) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10586345 + 10586346.

It is an arithmetic number, because the mean of its divisors is an integer number (10586346).

Almost surely, 2^21172691 is an apocalyptic number.

21172691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21172691 is an equidigital number, since it uses as much as digits as its factorization.

21172691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1512, while the sum is 29.

The square root of 21172691 is about 4601.3792497468. The cubic root of 21172691 is about 276.6466102136.

The spelling of 21172691 in words is "twenty-one million, one hundred seventy-two thousand, six hundred ninety-one".