191881721 has 2 divisors, whose sum is σ = 191881722. Its totient is φ = 191881720.

The previous prime is 191881699. The next prime is 191881733. The reversal of 191881721 is 127188191.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 109725625 + 82156096 = 10475^2 + 9064^2 .

It is a cyclic number.

It is not a de Polignac number, because 191881721 - 2¹⁴ = 191865337 is a prime.

It is not a weakly prime, because it can be changed into another prime (191881751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 95940860 + 95940861.

It is an arithmetic number, because the mean of its divisors is an integer number (95940861).

Almost surely, 2^191881721 is an apocalyptic number.

It is an amenable number.

191881721 is a deficient number, since it is larger than the sum of its proper divisors (1).

191881721 is an equidigital number, since it uses as much as digits as its factorization.

191881721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 38.

The square root of 191881721 is about 13852.1377772530. The cubic root of 191881721 is about 576.7813400130.

The spelling of 191881721 in words is "one hundred ninety-one million, eight hundred eighty-one thousand, seven hundred twenty-one".