821551 has 2 divisors, whose sum is σ = 821552. Its totient is φ = 821550.

The previous prime is 821519. The next prime is 821573. The reversal of 821551 is 155128.

821551 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an a-pointer prime, because the next prime (821573) can be obtained adding 821551 to its sum of digits (22).

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 821551 - 2⁵ = 821519 is a prime.

It is equal to p₆₅₅₃₃ and since 821551 and 65533 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (821651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410775 + 410776.

It is an arithmetic number, because the mean of its divisors is an integer number (410776).

2⁸²¹⁵⁵¹ is an apocalyptic number.

821551 is a deficient number, since it is larger than the sum of its proper divisors (1).

821551 is an equidigital number, since it uses as much as digits as its factorization.

821551 is an evil number, because the sum of its binary digits is even.

The product of its digits is 400, while the sum is 22.

The square root of 821551 is about 906.3945057203. The cubic root of 821551 is about 93.6579921017.

Adding to 821551 its reverse (155128), we get a palindrome (976679).

The spelling of 821551 in words is "eight hundred twenty-one thousand, five hundred fifty-one".