19961581 has 2 divisors, whose sum is σ = 19961582. Its totient is φ = 19961580.

The previous prime is 19961573. The next prime is 19961593. The reversal of 19961581 is 18516991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18139081 + 1822500 = 4259^2 + 1350^2 .

It is a cyclic number.

It is not a de Polignac number, because 19961581 - 2³ = 19961573 is a prime.

It is a super-2 number, since 2×19961581² = 796929432039122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19961681) 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 as a sum of consecutive naturals, namely, 9980790 + 9980791.

It is an arithmetic number, because the mean of its divisors is an integer number (9980791).

Almost surely, 2^19961581 is an apocalyptic number.

It is an amenable number.

19961581 is a deficient number, since it is larger than the sum of its proper divisors (1).

19961581 is an equidigital number, since it uses as much as digits as its factorization.

19961581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 19440, while the sum is 40.

The square root of 19961581 is about 4467.8385154345. The cubic root of 19961581 is about 271.2678415640.

The spelling of 19961581 in words is "nineteen million, nine hundred sixty-one thousand, five hundred eighty-one".