21378361 has 2 divisors, whose sum is σ = 21378362. Its totient is φ = 21378360.

The previous prime is 21378359. The next prime is 21378389. The reversal of 21378361 is 16387312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11861136 + 9517225 = 3444^2 + 3085^2 .

It is a cyclic number.

It is not a de Polignac number, because 21378361 - 2¹ = 21378359 is a prime.

Together with 21378359, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21373361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10689180 + 10689181.

It is an arithmetic number, because the mean of its divisors is an integer number (10689181).

Almost surely, 2^21378361 is an apocalyptic number.

It is an amenable number.

21378361 is a deficient number, since it is larger than the sum of its proper divisors (1).

21378361 is an equidigital number, since it uses as much as digits as its factorization.

21378361 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6048, while the sum is 31.

The square root of 21378361 is about 4623.6739720703. The cubic root of 21378361 is about 277.5395003696.

The spelling of 21378361 in words is "twenty-one million, three hundred seventy-eight thousand, three hundred sixty-one".