81961965 has 12 divisors (see below), whose sum is σ = 142067484. Its totient is φ = 43713024.

The previous prime is 81961961. The next prime is 81961967. The reversal of 81961965 is 56916918.

It can be written as a sum of positive squares in 2 ways, for example, as 55398249 + 26563716 = 7443^2 + 5154^2 .

It is not a de Polignac number, because 81961965 - 2² = 81961961 is a prime.

It is a super-2 number, since 2×81961965² = 13435527413322450, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45), and also a Moran number because the ratio is a prime number: 1821377 = 81961965 / (8 + 1 + 9 + 6 + 1 + 9 + 6 + 5).

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 81961965.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81961961) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 910644 + ... + 910733.

It is an arithmetic number, because the mean of its divisors is an integer number (11838957).

Almost surely, 2^81961965 is an apocalyptic number.

It is an amenable number.

81961965 is a deficient number, since it is larger than the sum of its proper divisors (60105519).

81961965 is a wasteful number, since it uses less digits than its factorization.

81961965 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1821388 (or 1821385 counting only the distinct ones).

The product of its digits is 116640, while the sum is 45.

The square root of 81961965 is about 9053.2847630018. The cubic root of 81961965 is about 434.3809665002.

The spelling of 81961965 in words is "eighty-one million, nine hundred sixty-one thousand, nine hundred sixty-five".