161721538 has 16 divisors (see below), whose sum is σ = 270791136. Its totient is φ = 71799840.

The previous prime is 161721491. The next prime is 161721563. The reversal of 161721538 is 835127161.

It is a happy number.

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 7 ways as a sum of consecutive naturals, for example, 84531 + ... + 86422.

It is an arithmetic number, because the mean of its divisors is an integer number (16924446).

Almost surely, 2^161721538 is an apocalyptic number.

161721538 is a deficient number, since it is larger than the sum of its proper divisors (109069598).

161721538 is a wasteful number, since it uses less digits than its factorization.

161721538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171009.

The product of its digits is 10080, while the sum is 34.

The square root of 161721538 is about 12716.9783360671. The cubic root of 161721538 is about 544.8236536321.

Adding to 161721538 its reverse (835127161), we get a palindrome (996848699).

The spelling of 161721538 in words is "one hundred sixty-one million, seven hundred twenty-one thousand, five hundred thirty-eight".