21259691 has 2 divisors, whose sum is σ = 21259692. Its totient is φ = 21259690.

The previous prime is 21259681. The next prime is 21259699. The reversal of 21259691 is 19695212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21259691 - 2⁶ = 21259627 is a prime.

It is a super-2 number, since 2×21259691² = 903948922830962, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21259699) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10629845 + 10629846.

It is an arithmetic number, because the mean of its divisors is an integer number (10629846).

Almost surely, 2^21259691 is an apocalyptic number.

21259691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21259691 is an equidigital number, since it uses as much as digits as its factorization.

21259691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9720, while the sum is 35.

The square root of 21259691 is about 4610.8232453652. The cubic root of 21259691 is about 277.0250121862.

The spelling of 21259691 in words is "twenty-one million, two hundred fifty-nine thousand, six hundred ninety-one".