21016409 has 2 divisors, whose sum is σ = 21016410. Its totient is φ = 21016408.

The previous prime is 21016397. The next prime is 21016417. The reversal of 21016409 is 90461012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14462809 + 6553600 = 3803^2 + 2560^2 .

It is a cyclic number.

It is not a de Polignac number, because 21016409 - 2⁴ = 21016393 is a prime.

It is not a weakly prime, because it can be changed into another prime (21016439) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10508204 + 10508205.

It is an arithmetic number, because the mean of its divisors is an integer number (10508205).

Almost surely, 2^21016409 is an apocalyptic number.

It is an amenable number.

21016409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21016409 is an equidigital number, since it uses as much as digits as its factorization.

21016409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 21016409 is about 4584.3657140329. The cubic root of 21016409 is about 275.9642579565.

The spelling of 21016409 in words is "twenty-one million, sixteen thousand, four hundred nine".