21697451 has 2 divisors, whose sum is σ = 21697452. Its totient is φ = 21697450.

The previous prime is 21697439. The next prime is 21697453. The reversal of 21697451 is 15479612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21697451 - 2¹⁰ = 21696427 is a prime.

It is a Sophie Germain prime.

Together with 21697453, 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 (21697453) 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, 10848725 + 10848726.

It is an arithmetic number, because the mean of its divisors is an integer number (10848726).

Almost surely, 2^21697451 is an apocalyptic number.

21697451 is a deficient number, since it is larger than the sum of its proper divisors (1).

21697451 is an equidigital number, since it uses as much as digits as its factorization.

21697451 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15120, while the sum is 35.

The square root of 21697451 is about 4658.0522753615. The cubic root of 21697451 is about 278.9135234705.

The spelling of 21697451 in words is "twenty-one million, six hundred ninety-seven thousand, four hundred fifty-one".