21681619 has 2 divisors, whose sum is σ = 21681620. Its totient is φ = 21681618.

The previous prime is 21681599. The next prime is 21681643. The reversal of 21681619 is 91618612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21681619 - 2¹⁷ = 21550547 is a prime.

It is a super-2 number, since 2×21681619² = 940185204922322, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21681659) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10840809 + 10840810.

It is an arithmetic number, because the mean of its divisors is an integer number (10840810).

Almost surely, 2^21681619 is an apocalyptic number.

21681619 is a deficient number, since it is larger than the sum of its proper divisors (1).

21681619 is an equidigital number, since it uses as much as digits as its factorization.

21681619 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5184, while the sum is 34.

The square root of 21681619 is about 4656.3525424950. The cubic root of 21681619 is about 278.8456685973.

The spelling of 21681619 in words is "twenty-one million, six hundred eighty-one thousand, six hundred nineteen".