778561 has 6 divisors (see below), whose sum is σ = 905730. Its totient is φ = 667296.

The previous prime is 778559. The next prime is 778567. The reversal of 778561 is 165877.

It can be written as a sum of positive squares in only one way, i.e., 571536 + 207025 = 756^2 + 455^2 .

It is not a de Polignac number, because 778561 - 2¹ = 778559 is a prime.

778561 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (778567) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 7896 + ... + 7993.

It is an arithmetic number, because the mean of its divisors is an integer number (150955).

2⁷⁷⁸⁵⁶¹ is an apocalyptic number.

It is an amenable number.

778561 is a deficient number, since it is larger than the sum of its proper divisors (127169).

778561 is a wasteful number, since it uses less digits than its factorization.

778561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15903 (or 15896 counting only the distinct ones).

The product of its digits is 11760, while the sum is 34.

The square root of 778561 is about 882.3610372178. The cubic root of 778561 is about 91.9949981528.

Adding to 778561 its product of digits (11760), we get a square (790321 = 889²).

The spelling of 778561 in words is "seven hundred seventy-eight thousand, five hundred sixty-one".