21779657 has 2 divisors, whose sum is σ = 21779658. Its totient is φ = 21779656.

The previous prime is 21779627. The next prime is 21779663. The reversal of 21779657 is 75697712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17131321 + 4648336 = 4139^2 + 2156^2 .

It is a cyclic number.

It is not a de Polignac number, because 21779657 - 2¹⁰ = 21778633 is a prime.

It is not a weakly prime, because it can be changed into another prime (21779627) 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, 10889828 + 10889829.

It is an arithmetic number, because the mean of its divisors is an integer number (10889829).

Almost surely, 2^21779657 is an apocalyptic number.

It is an amenable number.

21779657 is a deficient number, since it is larger than the sum of its proper divisors (1).

21779657 is an equidigital number, since it uses as much as digits as its factorization.

21779657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 185220, while the sum is 44.

The square root of 21779657 is about 4666.8680075614. The cubic root of 21779657 is about 279.2653231568.

The spelling of 21779657 in words is "twenty-one million, seven hundred seventy-nine thousand, six hundred fifty-seven".