21778457 has 2 divisors, whose sum is σ = 21778458. Its totient is φ = 21778456.

The previous prime is 21778441. The next prime is 21778481. The reversal of 21778457 is 75487712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20620681 + 1157776 = 4541^2 + 1076^2 .

It is a cyclic number.

It is not a de Polignac number, because 21778457 - 2⁴ = 21778441 is a prime.

It is not a weakly prime, because it can be changed into another prime (21778157) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10889228 + 10889229.

It is an arithmetic number, because the mean of its divisors is an integer number (10889229).

Almost surely, 2^21778457 is an apocalyptic number.

It is an amenable number.

21778457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21778457 is an equidigital number, since it uses as much as digits as its factorization.

21778457 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 109760, while the sum is 41.

The square root of 21778457 is about 4666.7394399088. The cubic root of 21778457 is about 279.2601941421.

The spelling of 21778457 in words is "twenty-one million, seven hundred seventy-eight thousand, four hundred fifty-seven".