21078949 has 2 divisors, whose sum is σ = 21078950. Its totient is φ = 21078948.

The previous prime is 21078947. The next prime is 21078991. The reversal of 21078949 is 94987012.

21078949 is nontrivially palindromic in base 7.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11437924 + 9641025 = 3382^2 + 3105^2 .

It is a cyclic number.

It is not a de Polignac number, because 21078949 - 2¹ = 21078947 is a prime.

Together with 21078947, it forms a pair of twin primes.

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

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21078947) 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, 10539474 + 10539475.

It is an arithmetic number, because the mean of its divisors is an integer number (10539475).

Almost surely, 2^21078949 is an apocalyptic number.

It is an amenable number.

21078949 is a deficient number, since it is larger than the sum of its proper divisors (1).

21078949 is an equidigital number, since it uses as much as digits as its factorization.

21078949 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36288, while the sum is 40.

The square root of 21078949 is about 4591.1816561752. The cubic root of 21078949 is about 276.2377222692.

The spelling of 21078949 in words is "twenty-one million, seventy-eight thousand, nine hundred forty-nine".