167991721 has 2 divisors, whose sum is σ = 167991722. Its totient is φ = 167991720.

The previous prime is 167991709. The next prime is 167991731. The reversal of 167991721 is 127199761.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 159668496 + 8323225 = 12636^2 + 2885^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-167991721 is a prime.

It is not a weakly prime, because it can be changed into another prime (167991731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83995860 + 83995861.

It is an arithmetic number, because the mean of its divisors is an integer number (83995861).

Almost surely, 2^167991721 is an apocalyptic number.

It is an amenable number.

167991721 is a deficient number, since it is larger than the sum of its proper divisors (1).

167991721 is an equidigital number, since it uses as much as digits as its factorization.

167991721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 47628, while the sum is 43.

The square root of 167991721 is about 12961.1620235224. The cubic root of 167991721 is about 551.7757711856.

The spelling of 167991721 in words is "one hundred sixty-seven million, nine hundred ninety-one thousand, seven hundred twenty-one".