21015913 has 2 divisors, whose sum is σ = 21015914. Its totient is φ = 21015912.

The previous prime is 21015871. The next prime is 21015941. The reversal of 21015913 is 31951012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12652249 + 8363664 = 3557^2 + 2892^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21015913 is a prime.

It is not a weakly prime, because it can be changed into another prime (21015013) 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, 10507956 + 10507957.

It is an arithmetic number, because the mean of its divisors is an integer number (10507957).

Almost surely, 2^21015913 is an apocalyptic number.

It is an amenable number.

21015913 is a deficient number, since it is larger than the sum of its proper divisors (1).

21015913 is an equidigital number, since it uses as much as digits as its factorization.

21015913 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 270, while the sum is 22.

The square root of 21015913 is about 4584.3116168079. The cubic root of 21015913 is about 275.9620869648.

Adding to 21015913 its reverse (31951012), we get a palindrome (52966925).

The spelling of 21015913 in words is "twenty-one million, fifteen thousand, nine hundred thirteen".