21609919 has 2 divisors, whose sum is σ = 21609920. Its totient is φ = 21609918.

The previous prime is 21609899. The next prime is 21609923. The reversal of 21609919 is 91990612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21609919 - 2⁹ = 21609407 is a prime.

It is a super-2 number, since 2×21609919² = 933977198373122, which contains 22 as substring.

It is a plaindrome in base 8.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21609019) 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, 10804959 + 10804960.

It is an arithmetic number, because the mean of its divisors is an integer number (10804960).

Almost surely, 2^21609919 is an apocalyptic number.

21609919 is a deficient number, since it is larger than the sum of its proper divisors (1).

21609919 is an equidigital number, since it uses as much as digits as its factorization.

21609919 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8748, while the sum is 37.

The square root of 21609919 is about 4648.6470074636. The cubic root of 21609919 is about 278.5379530483.

The spelling of 21609919 in words is "twenty-one million, six hundred nine thousand, nine hundred nineteen".