21019409 has 2 divisors, whose sum is σ = 21019410. Its totient is φ = 21019408.

The previous prime is 21019393. The next prime is 21019459. The reversal of 21019409 is 90491012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14992384 + 6027025 = 3872^2 + 2455^2 .

It is a cyclic number.

It is not a de Polignac number, because 21019409 - 2⁴ = 21019393 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21019459) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509704 + 10509705.

It is an arithmetic number, because the mean of its divisors is an integer number (10509705).

Almost surely, 2^21019409 is an apocalyptic number.

It is an amenable number.

21019409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21019409 is an equidigital number, since it uses as much as digits as its factorization.

21019409 is an evil number, because the sum of its binary digits is even.

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

The square root of 21019409 is about 4584.6929013839. The cubic root of 21019409 is about 275.9773882267.

The spelling of 21019409 in words is "twenty-one million, nineteen thousand, four hundred nine".