21516403 has 2 divisors, whose sum is σ = 21516404. Its totient is φ = 21516402.

The previous prime is 21516359. The next prime is 21516421. The reversal of 21516403 is 30461512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21516403 - 2²¹ = 19419251 is a prime.

It is not a weakly prime, because it can be changed into another prime (21516433) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10758201 + 10758202.

It is an arithmetic number, because the mean of its divisors is an integer number (10758202).

Almost surely, 2^21516403 is an apocalyptic number.

21516403 is a deficient number, since it is larger than the sum of its proper divisors (1).

21516403 is an equidigital number, since it uses as much as digits as its factorization.

21516403 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21516403 is about 4638.5776914912. The cubic root of 21516403 is about 278.1355850535.

Adding to 21516403 its reverse (30461512), we get a palindrome (51977915).

The spelling of 21516403 in words is "twenty-one million, five hundred sixteen thousand, four hundred three".