21691519 has 2 divisors, whose sum is σ = 21691520. Its totient is φ = 21691518.

The previous prime is 21691517. The next prime is 21691529. The reversal of 21691519 is 91519612.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21691519 - 2¹ = 21691517 is a prime.

It is a super-2 number, since 2×21691519² = 941043993054722, which contains 22 as substring.

Together with 21691517, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21691513) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845759 + 10845760.

It is an arithmetic number, because the mean of its divisors is an integer number (10845760).

Almost surely, 2^21691519 is an apocalyptic number.

21691519 is a deficient number, since it is larger than the sum of its proper divisors (1).

21691519 is an equidigital number, since it uses as much as digits as its factorization.

21691519 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4860, while the sum is 34.

The square root of 21691519 is about 4657.4154850088. The cubic root of 21691519 is about 278.8881031907. Note that the first 3 decimals are identical.

The spelling of 21691519 in words is "twenty-one million, six hundred ninety-one thousand, five hundred nineteen".