161237457721 has 4 divisors (see below), whose sum is σ = 161960495872. Its totient is φ = 160514419572.

The previous prime is 161237457713. The next prime is 161237457743. The reversal of 161237457721 is 127754732161.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 127754732161 = 7 ⋅18250676023.

It is a cyclic number.

It is not a de Polignac number, because 161237457721 - 2³ = 161237457713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (161237452721) 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, 361518741 + ... + 361519186.

It is an arithmetic number, because the mean of its divisors is an integer number (40490123968).

Almost surely, 2^161237457721 is an apocalyptic number.

It is an amenable number.

161237457721 is a deficient number, since it is larger than the sum of its proper divisors (723038151).

161237457721 is an equidigital number, since it uses as much as digits as its factorization.

161237457721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 723038150.

The product of its digits is 493920, while the sum is 46.

The spelling of 161237457721 in words is "one hundred sixty-one billion, two hundred thirty-seven million, four hundred fifty-seven thousand, seven hundred twenty-one".