81371640 has 128 divisors (see below), whose sum is σ = 283023360. Its totient is φ = 18330624.

The previous prime is 81371629. The next prime is 81371657. The reversal of 81371640 is 4617318.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 81371598 and 81371607.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 60657 + ... + 61983.

It is an arithmetic number, because the mean of its divisors is an integer number (2211120).

Almost surely, 2^81371640 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81371640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (141511680).

81371640 is an abundant number, since it is smaller than the sum of its proper divisors (201651720).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81371640 is a wasteful number, since it uses less digits than its factorization.

81371640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1421 (or 1417 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 30.

The square root of 81371640 is about 9020.6230383494. The cubic root of 81371640 is about 433.3355871020.

Adding to 81371640 its reverse (4617318), we get a palindrome (85988958).

The spelling of 81371640 in words is "eighty-one million, three hundred seventy-one thousand, six hundred forty".