820421509 has 2 divisors, whose sum is σ = 820421510. Its totient is φ = 820421508.

The previous prime is 820421447. The next prime is 820421561. The reversal of 820421509 is 905124028.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 441924484 + 378497025 = 21022^2 + 19455^2 .

It is a cyclic number.

It is not a de Polignac number, because 820421509 - 2¹¹ = 820419461 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (820421579) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410210754 + 410210755.

It is an arithmetic number, because the mean of its divisors is an integer number (410210755).

Almost surely, 2^820421509 is an apocalyptic number.

It is an amenable number.

820421509 is a deficient number, since it is larger than the sum of its proper divisors (1).

820421509 is an equidigital number, since it uses as much as digits as its factorization.

820421509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5760, while the sum is 31.

The square root of 820421509 is about 28643.0010473763. The cubic root of 820421509 is about 936.1505121906.

The spelling of 820421509 in words is "eight hundred twenty million, four hundred twenty-one thousand, five hundred nine".