1916721581 has 2 divisors, whose sum is σ = 1916721582. Its totient is φ = 1916721580.

The previous prime is 1916721551. The next prime is 1916721589. The reversal of 1916721581 is 1851276191.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1567368100 + 349353481 = 39590^2 + 18691^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1916721581 is a prime.

It is a super-2 number, since 2×1916721581² = 7347643238142279122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1916721589) 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, 958360790 + 958360791.

It is an arithmetic number, because the mean of its divisors is an integer number (958360791).

Almost surely, 2^1916721581 is an apocalyptic number.

It is an amenable number.

1916721581 is a deficient number, since it is larger than the sum of its proper divisors (1).

1916721581 is an equidigital number, since it uses as much as digits as its factorization.

1916721581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 30240, while the sum is 41.

The square root of 1916721581 is about 43780.3789499360. The cubic root of 1916721581 is about 1242.1851819914.

The spelling of 1916721581 in words is "one billion, nine hundred sixteen million, seven hundred twenty-one thousand, five hundred eighty-one".