81637643 has 4 divisors (see below), whose sum is σ = 81713160. Its totient is φ = 81562128.

The previous prime is 81637631. The next prime is 81637657. The reversal of 81637643 is 34673618.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81637643 - 2¹² = 81633547 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81637597 and 81637606.

It is not an unprimeable number, because it can be changed into a prime (81637943) 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, 36113 + ... + 38306.

It is an arithmetic number, because the mean of its divisors is an integer number (20428290).

Almost surely, 2^81637643 is an apocalyptic number.

81637643 is a deficient number, since it is larger than the sum of its proper divisors (75517).

81637643 is a wasteful number, since it uses less digits than its factorization.

81637643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75516.

The product of its digits is 72576, while the sum is 38.

The square root of 81637643 is about 9035.3551673412. The cubic root of 81637643 is about 433.8072632695.

The spelling of 81637643 in words is "eighty-one million, six hundred thirty-seven thousand, six hundred forty-three".