81209520 has 320 divisors, whose sum is σ = 329978880. Its totient is φ = 17971200.

The previous prime is 81209519. The next prime is 81209521. The reversal of 81209520 is 2590218.

It is an interprime number because it is at equal distance from previous prime (81209519) and next prime (81209521).

It is a super-2 number, since 2×81209520² = 13189972277260800, which contains 22 as substring.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81209521) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 619855 + ... + 619985.

It is an arithmetic number, because the mean of its divisors is an integer number (1031184).

Almost surely, 2^81209520 is an apocalyptic number.

81209520 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81209520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (164989440).

81209520 is an abundant number, since it is smaller than the sum of its proper divisors (248769360).

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

81209520 is a wasteful number, since it uses less digits than its factorization.

81209520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201 (or 189 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 81209520 is about 9011.6324825195. The cubic root of 81209520 is about 433.0476117803.

Adding to 81209520 its reverse (2590218), we get a palindrome (83799738).

The spelling of 81209520 in words is "eighty-one million, two hundred nine thousand, five hundred twenty".