81891019402 has 8 divisors (see below), whose sum is σ = 122848258212. Its totient is φ = 40941600000.

The previous prime is 81891019367. The next prime is 81891019409. The reversal of 81891019402 is 20491019818.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 66522210561 + 15368808841 = 257919^2 + 123971^2 .

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

It is a super-2 number, since 2×81891019402² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81891019409) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1928599 + ... + 1970602.

Almost surely, 2^81891019402 is an apocalyptic number.

81891019402 is a deficient number, since it is larger than the sum of its proper divisors (40957238810).

81891019402 is a wasteful number, since it uses less digits than its factorization.

81891019402 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3909704.

The product of its (nonzero) digits is 41472, while the sum is 43.

The spelling of 81891019402 in words is "eighty-one billion, eight hundred ninety-one million, nineteen thousand, four hundred two".