161981551 has 4 divisors (see below), whose sum is σ = 162502704. Its totient is φ = 161460400.

The previous prime is 161981537. The next prime is 161981563. The reversal of 161981551 is 155189161.

161981551 = T₃₈₈ + T₃₈₉ + ... + T₁₀₀₉.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 161981551 - 2¹³ = 161973359 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 161981551.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161981531) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 260110 + ... + 260731.

It is an arithmetic number, because the mean of its divisors is an integer number (40625676).

Almost surely, 2^161981551 is an apocalyptic number.

161981551 is a deficient number, since it is larger than the sum of its proper divisors (521153).

161981551 is an equidigital number, since it uses as much as digits as its factorization.

161981551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 521152.

The product of its digits is 10800, while the sum is 37.

The square root of 161981551 is about 12727.1972955557. The cubic root of 161981551 is about 545.1154832012.

The spelling of 161981551 in words is "one hundred sixty-one million, nine hundred eighty-one thousand, five hundred fifty-one".