161721540 has 72 divisors (see below), whose sum is σ = 516384960. Its totient is φ = 40855104.

The previous prime is 161721491. The next prime is 161721563. The reversal of 161721540 is 45127161.

It is a happy number.

161721540 is a `hidden beast` number, since 1 + 617 + 2 + 1 + 5 + 40 = 666.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 20224 + ... + 27063.

Almost surely, 2^161721540 is an apocalyptic number.

161721540 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

161721540 is an abundant number, since it is smaller than the sum of its proper divisors (354663420).

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

161721540 is a wasteful number, since it uses less digits than its factorization.

161721540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 47321 (or 47316 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 161721540 is about 12716.9784147021. The cubic root of 161721540 is about 544.8236558780.

It can be divided in two parts, 161721 and 540, that added together give a palindrome (162261).

The spelling of 161721540 in words is "one hundred sixty-one million, seven hundred twenty-one thousand, five hundred forty".