21865619 has 2 divisors, whose sum is σ = 21865620. Its totient is φ = 21865618.

The previous prime is 21865589. The next prime is 21865639. The reversal of 21865619 is 91656812.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21865619 is a prime.

It is a super-2 number, since 2×21865619² = 956210588506322, which contains 22 as substring.

It is a Sophie Germain prime.

It is not a weakly prime, because it can be changed into another prime (21865639) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932809 + 10932810.

It is an arithmetic number, because the mean of its divisors is an integer number (10932810).

Almost surely, 2^21865619 is an apocalyptic number.

21865619 is a deficient number, since it is larger than the sum of its proper divisors (1).

21865619 is an equidigital number, since it uses as much as digits as its factorization.

21865619 is an evil number, because the sum of its binary digits is even.

The product of its digits is 25920, while the sum is 38.

The square root of 21865619 is about 4676.0687548410. The cubic root of 21865619 is about 279.6322510575.

The spelling of 21865619 in words is "twenty-one million, eight hundred sixty-five thousand, six hundred nineteen".