81997406 has 4 divisors (see below), whose sum is σ = 122996112. Its totient is φ = 40998702.

The previous prime is 81997381. The next prime is 81997427. The reversal of 81997406 is 60479918.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 60479918 = 2 ⋅30239959.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20499350 + ... + 20499353.

It is an arithmetic number, because the mean of its divisors is an integer number (30749028).

Almost surely, 2^81997406 is an apocalyptic number.

81997406 is a deficient number, since it is larger than the sum of its proper divisors (40998706).

81997406 is a wasteful number, since it uses less digits than its factorization.

81997406 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40998705.

The product of its (nonzero) digits is 108864, while the sum is 44.

The square root of 81997406 is about 9055.2419073153. The cubic root of 81997406 is about 434.4435673965.

The spelling of 81997406 in words is "eighty-one million, nine hundred ninety-seven thousand, four hundred six".