21378521 has 2 divisors, whose sum is σ = 21378522. Its totient is φ = 21378520.

The previous prime is 21378491. The next prime is 21378527. The reversal of 21378521 is 12587312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13980121 + 7398400 = 3739^2 + 2720^2 .

It is a cyclic number.

It is not a de Polignac number, because 21378521 - 2⁶ = 21378457 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21378527) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10689260 + 10689261.

It is an arithmetic number, because the mean of its divisors is an integer number (10689261).

Almost surely, 2^21378521 is an apocalyptic number.

It is an amenable number.

21378521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21378521 is an equidigital number, since it uses as much as digits as its factorization.

21378521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3360, while the sum is 29.

The square root of 21378521 is about 4623.6912742959. The cubic root of 21378521 is about 277.5401927552.

The spelling of 21378521 in words is "twenty-one million, three hundred seventy-eight thousand, five hundred twenty-one".