66781581 has 16 divisors (see below), whose sum is σ = 93137280. Its totient is φ = 42482880.

The previous prime is 66781571. The next prime is 66781601. The reversal of 66781581 is 18518766.

It is not a de Polignac number, because 66781581 - 2⁷ = 66781453 is a prime.

It is a super-2 number, since 2×66781581² = 8919559121719122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66781541) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36435 + ... + 38223.

It is an arithmetic number, because the mean of its divisors is an integer number (5821080).

Almost surely, 2^66781581 is an apocalyptic number.

It is an amenable number.

66781581 is a deficient number, since it is larger than the sum of its proper divisors (26355699).

66781581 is a wasteful number, since it uses less digits than its factorization.

66781581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2356.

The product of its digits is 80640, while the sum is 42.

The square root of 66781581 is about 8171.9998164464. Note that the first 3 decimals coincide. The cubic root of 66781581 is about 405.7129766999.

The spelling of 66781581 in words is "sixty-six million, seven hundred eighty-one thousand, five hundred eighty-one".