21605777 has 2 divisors, whose sum is σ = 21605778. Its totient is φ = 21605776.

The previous prime is 21605747. The next prime is 21605803. The reversal of 21605777 is 77750612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11082241 + 10523536 = 3329^2 + 3244^2 .

It is a cyclic number.

It is not a de Polignac number, because 21605777 - 2¹⁸ = 21343633 is a prime.

It is a Chen prime.

It is a zygodrome in base 3.

It is not a weakly prime, because it can be changed into another prime (21605747) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802888 + 10802889.

It is an arithmetic number, because the mean of its divisors is an integer number (10802889).

Almost surely, 2^21605777 is an apocalyptic number.

It is an amenable number.

21605777 is a deficient number, since it is larger than the sum of its proper divisors (1).

21605777 is an equidigital number, since it uses as much as digits as its factorization.

21605777 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 20580, while the sum is 35.

The square root of 21605777 is about 4648.2014801426. The cubic root of 21605777 is about 278.5201560061.

The spelling of 21605777 in words is "twenty-one million, six hundred five thousand, seven hundred seventy-seven".