81212040 has 384 divisors, whose sum is σ = 338607360. Its totient is φ = 16422912.

The previous prime is 81212039. The next prime is 81212041. The reversal of 81212040 is 4021218.

It is an interprime number because it is at equal distance from previous prime (81212039) and next prime (81212041).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81212041) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 1212087 + ... + 1212153.

It is an arithmetic number, because the mean of its divisors is an integer number (881790).

Almost surely, 2^81212040 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 81212040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (169303680).

81212040 is an abundant number, since it is smaller than the sum of its proper divisors (257395320).

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

81212040 is a wasteful number, since it uses less digits than its factorization.

81212040 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 141 (or 134 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 18.

The square root of 81212040 is about 9011.7723007187. The cubic root of 81212040 is about 433.0520910117.

Adding to 81212040 its reverse (4021218), we get a palindrome (85233258).

The spelling of 81212040 in words is "eighty-one million, two hundred twelve thousand, forty".