161721751 has 2 divisors, whose sum is σ = 161721752. Its totient is φ = 161721750.

The previous prime is 161721743. The next prime is 161721803. The reversal of 161721751 is 157127161.

It is a happy number.

It is a weak prime.

It is an emirp because it is prime and its reverse (157127161) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 161721751 - 2³ = 161721743 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (161721701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 80860875 + 80860876.

It is an arithmetic number, because the mean of its divisors is an integer number (80860876).

Almost surely, 2^161721751 is an apocalyptic number.

161721751 is a deficient number, since it is larger than the sum of its proper divisors (1).

161721751 is an equidigital number, since it uses as much as digits as its factorization.

161721751 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2940, while the sum is 31.

The square root of 161721751 is about 12716.9867106953. The cubic root of 161721751 is about 544.8238928238.

The spelling of 161721751 in words is "one hundred sixty-one million, seven hundred twenty-one thousand, seven hundred fifty-one".