21009403 has 2 divisors, whose sum is σ = 21009404. Its totient is φ = 21009402.

The previous prime is 21009389. The next prime is 21009407. The reversal of 21009403 is 30490012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21009403 - 2²¹ = 18912251 is a prime.

It is a plaindrome in base 13.

It is not a weakly prime, because it can be changed into another prime (21009407) 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, 10504701 + 10504702.

It is an arithmetic number, because the mean of its divisors is an integer number (10504702).

Almost surely, 2^21009403 is an apocalyptic number.

21009403 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009403 is an equidigital number, since it uses as much as digits as its factorization.

21009403 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 216, while the sum is 19.

The square root of 21009403 is about 4583.6015315470. The cubic root of 21009403 is about 275.9335895318.

Adding to 21009403 its reverse (30490012), we get a palindrome (51499415).

It can be divided in two parts, 21009 and 403, that added together give a palindrome (21412).

The spelling of 21009403 in words is "twenty-one million, nine thousand, four hundred three".