21178513 has 2 divisors, whose sum is σ = 21178514. Its totient is φ = 21178512.

The previous prime is 21178511. The next prime is 21178517. The reversal of 21178513 is 31587112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20684304 + 494209 = 4548^2 + 703^2 .

It is a cyclic number.

It is not a de Polignac number, because 21178513 - 2¹ = 21178511 is a prime.

Together with 21178511, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21178511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10589256 + 10589257.

It is an arithmetic number, because the mean of its divisors is an integer number (10589257).

Almost surely, 2^21178513 is an apocalyptic number.

It is an amenable number.

21178513 is a deficient number, since it is larger than the sum of its proper divisors (1).

21178513 is an equidigital number, since it uses as much as digits as its factorization.

21178513 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1680, while the sum is 28.

The square root of 21178513 is about 4602.0118426619. The cubic root of 21178513 is about 276.6719650281.

The spelling of 21178513 in words is "twenty-one million, one hundred seventy-eight thousand, five hundred thirteen".