81649780 has 12 divisors (see below), whose sum is σ = 171464580. Its totient is φ = 32659904.

The previous prime is 81649769. The next prime is 81649801. The reversal of 81649780 is 8794618.

It can be written as a sum of positive squares in 2 ways, for example, as 29203216 + 52446564 = 5404^2 + 7242^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2041225 + ... + 2041264.

It is an arithmetic number, because the mean of its divisors is an integer number (14288715).

Almost surely, 2^81649780 is an apocalyptic number.

It is an amenable number.

81649780 is an abundant number, since it is smaller than the sum of its proper divisors (89814800).

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

81649780 is a wasteful number, since it uses less digits than its factorization.

81649780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4082498 (or 4082496 counting only the distinct ones).

The product of its (nonzero) digits is 96768, while the sum is 43.

The square root of 81649780 is about 9036.0267817222. The cubic root of 81649780 is about 433.8287601251.

The spelling of 81649780 in words is "eighty-one million, six hundred forty-nine thousand, seven hundred eighty".