21864019 has 2 divisors, whose sum is σ = 21864020. Its totient is φ = 21864018.

The previous prime is 21864013. The next prime is 21864049. The reversal of 21864019 is 91046812.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21864019 - 2¹¹ = 21861971 is a prime.

It is a super-2 number, since 2×21864019² = 956070653664722, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21864013) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932009 + 10932010.

It is an arithmetic number, because the mean of its divisors is an integer number (10932010).

Almost surely, 2^21864019 is an apocalyptic number.

21864019 is a deficient number, since it is larger than the sum of its proper divisors (1).

21864019 is an equidigital number, since it uses as much as digits as its factorization.

21864019 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 21864019 is about 4675.8976678281. The cubic root of 21864019 is about 279.6254302656.

The spelling of 21864019 in words is "twenty-one million, eight hundred sixty-four thousand, nineteen".