21778973 has 2 divisors, whose sum is σ = 21778974. Its totient is φ = 21778972.

The previous prime is 21778969. The next prime is 21778979. The reversal of 21778973 is 37987712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13235044 + 8543929 = 3638^2 + 2923^2 .

It is a cyclic number.

It is not a de Polignac number, because 21778973 - 2² = 21778969 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21778979) 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, 10889486 + 10889487.

It is an arithmetic number, because the mean of its divisors is an integer number (10889487).

Almost surely, 2^21778973 is an apocalyptic number.

It is an amenable number.

21778973 is a deficient number, since it is larger than the sum of its proper divisors (1).

21778973 is an equidigital number, since it uses as much as digits as its factorization.

21778973 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 148176, while the sum is 44.

The square root of 21778973 is about 4666.7947244335. The cubic root of 21778973 is about 279.2623996415.

The spelling of 21778973 in words is "twenty-one million, seven hundred seventy-eight thousand, nine hundred seventy-three".