775916821 has 2 divisors, whose sum is σ = 775916822. Its totient is φ = 775916820.

The previous prime is 775916809. The next prime is 775916831. The reversal of 775916821 is 128619577.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 715295025 + 60621796 = 26745^2 + 7786^2 .

It is a cyclic number.

It is not a de Polignac number, because 775916821 - 2⁵ = 775916789 is a prime.

It is a super-2 number, since 2×775916821² = 1204093826221492082, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (775916831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 387958410 + 387958411.

It is an arithmetic number, because the mean of its divisors is an integer number (387958411).

Almost surely, 2^775916821 is an apocalyptic number.

It is an amenable number.

775916821 is a deficient number, since it is larger than the sum of its proper divisors (1).

775916821 is an equidigital number, since it uses as much as digits as its factorization.

775916821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 211680, while the sum is 46.

The square root of 775916821 is about 27855.2835383164. The cubic root of 775916821 is about 918.9073437093.

The spelling of 775916821 in words is "seven hundred seventy-five million, nine hundred sixteen thousand, eight hundred twenty-one".