161661220 has 24 divisors (see below), whose sum is σ = 387987264. Its totient is φ = 55426656.

The previous prime is 161661191. The next prime is 161661229. The reversal of 161661220 is 22166161.

It is a super-2 number, since 2×161661220² = 52268700103776800, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (161661229) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 577222 + ... + 577501.

It is an arithmetic number, because the mean of its divisors is an integer number (16166136).

Almost surely, 2^161661220 is an apocalyptic number.

161661220 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

161661220 is an abundant number, since it is smaller than the sum of its proper divisors (226326044).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

161661220 is a wasteful number, since it uses less digits than its factorization.

161661220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1154739 (or 1154737 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 25.

The square root of 161661220 is about 12714.6065609597. The cubic root of 161661220 is about 544.7559101102.

The spelling of 161661220 in words is "one hundred sixty-one million, six hundred sixty-one thousand, two hundred twenty".