21666019 has 2 divisors, whose sum is σ = 21666020. Its totient is φ = 21666018.

The previous prime is 21665989. The next prime is 21666037. The reversal of 21666019 is 91066612.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21666019 is a prime.

It is a super-2 number, since 2×21666019² = 938832758616722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21666049) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10833009 + 10833010.

It is an arithmetic number, because the mean of its divisors is an integer number (10833010).

Almost surely, 2^21666019 is an apocalyptic number.

21666019 is a deficient number, since it is larger than the sum of its proper divisors (1).

21666019 is an equidigital number, since it uses as much as digits as its factorization.

21666019 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 31.

The square root of 21666019 is about 4654.6771101764. The cubic root of 21666019 is about 278.7787757433.

The spelling of 21666019 in words is "twenty-one million, six hundred sixty-six thousand, nineteen".