161558821 has 2 divisors, whose sum is σ = 161558822. Its totient is φ = 161558820.

The previous prime is 161558807. The next prime is 161558849. The reversal of 161558821 is 128855161.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 84382596 + 77176225 = 9186^2 + 8785^2 .

It is an emirp because it is prime and its reverse (128855161) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 161558821 - 2¹³ = 161550629 is a prime.

It is a super-2 number, since 2×161558821² = 52202505285820082, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161558801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80779410 + 80779411.

It is an arithmetic number, because the mean of its divisors is an integer number (80779411).

Almost surely, 2^161558821 is an apocalyptic number.

It is an amenable number.

161558821 is a deficient number, since it is larger than the sum of its proper divisors (1).

161558821 is an equidigital number, since it uses as much as digits as its factorization.

161558821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19200, while the sum is 37.

The square root of 161558821 is about 12710.5790977437. The cubic root of 161558821 is about 544.6408665592.

It can be divided in two parts, 16155 and 8821, that added together give a triangular number (24976 = T₂₂₃).

The spelling of 161558821 in words is "one hundred sixty-one million, five hundred fifty-eight thousand, eight hundred twenty-one".