21678361 has 2 divisors, whose sum is σ = 21678362. Its totient is φ = 21678360.

The previous prime is 21678347. The next prime is 21678379. The reversal of 21678361 is 16387612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21678336 + 25 = 4656^2 + 5^2 .

It is a cyclic number.

It is not a de Polignac number, because 21678361 - 2⁵ = 21678329 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21678061) 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, 10839180 + 10839181.

It is an arithmetic number, because the mean of its divisors is an integer number (10839181).

Almost surely, 2^21678361 is an apocalyptic number.

It is an amenable number.

21678361 is a deficient number, since it is larger than the sum of its proper divisors (1).

21678361 is an equidigital number, since it uses as much as digits as its factorization.

21678361 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12096, while the sum is 34.

The square root of 21678361 is about 4656.0026847071. The cubic root of 21678361 is about 278.8317009335.

The spelling of 21678361 in words is "twenty-one million, six hundred seventy-eight thousand, three hundred sixty-one".