163721561 has 2 divisors, whose sum is σ = 163721562. Its totient is φ = 163721560.

The previous prime is 163721549. The next prime is 163721581. The reversal of 163721561 is 165127361.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 140873161 + 22848400 = 11869^2 + 4780^2 .

It is a cyclic number.

It is not a de Polignac number, because 163721561 - 2⁶ = 163721497 is a prime.

It is a Chen prime.

It is equal to p_9171437 and since 163721561 and 9171437 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (163721581) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 81860780 + 81860781.

It is an arithmetic number, because the mean of its divisors is an integer number (81860781).

Almost surely, 2^163721561 is an apocalyptic number.

It is an amenable number.

163721561 is a deficient number, since it is larger than the sum of its proper divisors (1).

163721561 is an equidigital number, since it uses as much as digits as its factorization.

163721561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7560, while the sum is 32.

The square root of 163721561 is about 12795.3726401383. The cubic root of 163721561 is about 547.0604170883.

The spelling of 163721561 in words is "one hundred sixty-three million, seven hundred twenty-one thousand, five hundred sixty-one".