21368513 has 2 divisors, whose sum is σ = 21368514. Its totient is φ = 21368512.

The previous prime is 21368497. The next prime is 21368527. The reversal of 21368513 is 31586312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21270544 + 97969 = 4612^2 + 313^2 .

It is a cyclic number.

It is not a de Polignac number, because 21368513 - 2⁴ = 21368497 is a prime.

It is a super-2 number, since 2×21368513² = 913226695662338, which contains 22 as substring.

It is equal to p_1351784 and since 21368513 and 1351784 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21368713) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10684256 + 10684257.

It is an arithmetic number, because the mean of its divisors is an integer number (10684257).

Almost surely, 2^21368513 is an apocalyptic number.

It is an amenable number.

21368513 is a deficient number, since it is larger than the sum of its proper divisors (1).

21368513 is an equidigital number, since it uses as much as digits as its factorization.

21368513 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 29.

The square root of 21368513 is about 4622.6088954183. The cubic root of 21368513 is about 277.4968773828.

The spelling of 21368513 in words is "twenty-one million, three hundred sixty-eight thousand, five hundred thirteen".