821257855551 has 72 divisors (see below), whose sum is σ = 1444176573840. Its totient is φ = 464984053632.

The previous prime is 821257855531. The next prime is 821257855609. The reversal of 821257855551 is 155558752128.

821257855551 is a `hidden beast` number, since 8 + 2 + 1 + 2 + 5 + 7 + 85 + 5 + 551 = 666.

It is not a de Polignac number, because 821257855551 - 2¹³ = 821257847359 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821257855531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 981475 + ... + 1614251.

It is an arithmetic number, because the mean of its divisors is an integer number (20058007970).

Almost surely, 2^821257855551 is an apocalyptic number.

821257855551 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

821257855551 is a deficient number, since it is larger than the sum of its proper divisors (622918718289).

821257855551 is a wasteful number, since it uses less digits than its factorization.

821257855551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 632915 (or 632896 counting only the distinct ones).

The product of its digits is 5600000, while the sum is 54.

It can be divided in two parts, 82125785 and 5551, that added together give a triangular number (82131336 = T₁₂₈₁₆).

The spelling of 821257855551 in words is "eight hundred twenty-one billion, two hundred fifty-seven million, eight hundred fifty-five thousand, five hundred fifty-one".