21375517 has 2 divisors, whose sum is σ = 21375518. Its totient is φ = 21375516.

The previous prime is 21375503. The next prime is 21375521. The reversal of 21375517 is 71557312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12489156 + 8886361 = 3534^2 + 2981^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21375517 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21375577) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10687758 + 10687759.

It is an arithmetic number, because the mean of its divisors is an integer number (10687759).

Almost surely, 2^21375517 is an apocalyptic number.

It is an amenable number.

21375517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21375517 is an equidigital number, since it uses as much as digits as its factorization.

21375517 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7350, while the sum is 31.

The square root of 21375517 is about 4623.3664142051. The cubic root of 21375517 is about 277.5271926387.

The spelling of 21375517 in words is "twenty-one million, three hundred seventy-five thousand, five hundred seventeen".