161661731 has 20 divisors (see below), whose sum is σ = 205772664. Its totient is φ = 125949600.

The previous prime is 161661707. The next prime is 161661739. The reversal of 161661731 is 137166161.

It is a de Polignac number, because none of the positive numbers 2^k-161661731 is a prime.

It is a super-2 number, since 2×161661731² = 52269030539832722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161661739) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 23351 + ... + 29471.

Almost surely, 2^161661731 is an apocalyptic number.

161661731 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

161661731 is a deficient number, since it is larger than the sum of its proper divisors (44110933).

161661731 is an frugal number, since it uses more digits than its factorization.

161661731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6160 (or 6139 counting only the distinct ones).

The product of its digits is 4536, while the sum is 32.

The square root of 161661731 is about 12714.6266559424. The cubic root of 161661731 is about 544.7564840883.

The spelling of 161661731 in words is "one hundred sixty-one million, six hundred sixty-one thousand, seven hundred thirty-one".