19891681 has 8 divisors (see below), whose sum is σ = 20540520. Its totient is φ = 19248768.

The previous prime is 19891679. The next prime is 19891687. The reversal of 19891681 is 18619891.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 17774656 + 2117025 = 4216^2 + 1455^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 19891681 - 2¹ = 19891679 is a prime.

It is a super-2 number, since 2×19891681² = 791357946011522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19891687) by changing a digit.

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, 5925 + ... + 8653.

It is an arithmetic number, because the mean of its divisors is an integer number (2567565).

Almost surely, 2^19891681 is an apocalyptic number.

It is an amenable number.

19891681 is a deficient number, since it is larger than the sum of its proper divisors (648839).

19891681 is a wasteful number, since it uses less digits than its factorization.

19891681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2963.

The product of its digits is 31104, while the sum is 43.

The square root of 19891681 is about 4460.0090807082. The cubic root of 19891681 is about 270.9508359772.

It can be divided in two parts, 198916 and 81, that multiplied together give a square (16112196 = 4014²).

The spelling of 19891681 in words is "nineteen million, eight hundred ninety-one thousand, six hundred eighty-one".