161651821 has 2 divisors, whose sum is σ = 161651822. Its totient is φ = 161651820.

The previous prime is 161651803. The next prime is 161651839. The reversal of 161651821 is 128156161.

161651821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a balanced prime because it is at equal distance from previous prime (161651803) and next prime (161651839).

It can be written as a sum of positive squares in only one way, i.e., 151634596 + 10017225 = 12314^2 + 3165^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-161651821 is a prime.

It is a super-2 number, since 2×161651821² = 52262622465232082, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161651801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80825910 + 80825911.

It is an arithmetic number, because the mean of its divisors is an integer number (80825911).

Almost surely, 2^161651821 is an apocalyptic number.

It is an amenable number.

161651821 is a deficient number, since it is larger than the sum of its proper divisors (1).

161651821 is an equidigital number, since it uses as much as digits as its factorization.

161651821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2880, while the sum is 31.

The square root of 161651821 is about 12714.2369413190. The cubic root of 161651821 is about 544.7453525173.

The spelling of 161651821 in words is "one hundred sixty-one million, six hundred fifty-one thousand, eight hundred twenty-one".