21481409 has 2 divisors, whose sum is σ = 21481410. Its totient is φ = 21481408.

The previous prime is 21481403. The next prime is 21481459. The reversal of 21481409 is 90418412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21298225 + 183184 = 4615^2 + 428^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21481409 is a prime.

It is a super-2 number, since 2×21481409² = 922901865250562, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21481403) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10740704 + 10740705.

It is an arithmetic number, because the mean of its divisors is an integer number (10740705).

Almost surely, 2^21481409 is an apocalyptic number.

It is an amenable number.

21481409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21481409 is an equidigital number, since it uses as much as digits as its factorization.

21481409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 21481409 is about 4634.8040951048. The cubic root of 21481409 is about 277.9847178598.

The spelling of 21481409 in words is "twenty-one million, four hundred eighty-one thousand, four hundred nine".