21661019 has 4 divisors (see below), whose sum is σ = 21696744. Its totient is φ = 21625296.

The previous prime is 21661001. The next prime is 21661027. The reversal of 21661019 is 91016612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21661019 - 2¹² = 21656923 is a prime.

It is a super-2 number, since 2×21661019² = 938399488236722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21666019) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16937 + ... + 18170.

It is an arithmetic number, because the mean of its divisors is an integer number (5424186).

Almost surely, 2^21661019 is an apocalyptic number.

21661019 is a deficient number, since it is larger than the sum of its proper divisors (35725).

21661019 is an equidigital number, since it uses as much as digits as its factorization.

21661019 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35724.

The product of its (nonzero) digits is 648, while the sum is 26.

The square root of 21661019 is about 4654.1399850026. The cubic root of 21661019 is about 278.7573289312.

The spelling of 21661019 in words is "twenty-one million, six hundred sixty-one thousand, nineteen".