21240019 has 4 divisors (see below), whose sum is σ = 21508960. Its totient is φ = 20971080.

The previous prime is 21240001. The next prime is 21240049. The reversal of 21240019 is 91004212.

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 21240019 - 2⁹ = 21239507 is a prime.

It is a super-2 number, since 2×21240019² = 902276814240722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21239978 and 21240005.

It is not an unprimeable number, because it can be changed into a prime (21240049) 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, 134352 + ... + 134509.

It is an arithmetic number, because the mean of its divisors is an integer number (5377240).

Almost surely, 2^21240019 is an apocalyptic number.

21240019 is a deficient number, since it is larger than the sum of its proper divisors (268941).

21240019 is an equidigital number, since it uses as much as digits as its factorization.

21240019 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268940.

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21240019 is about 4608.6895100451. The cubic root of 21240019 is about 276.9395402981.

The spelling of 21240019 in words is "twenty-one million, two hundred forty thousand, nineteen".