66801781 has 4 divisors (see below), whose sum is σ = 66828064.
Its totient is φ = 66775500.
The previous prime is 66801769. The next prime is 66801793. The reversal of 66801781 is 18710866.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18710866 = 2 ⋅9355433.
It is an interprime number because it is at equal distance from previous prime (66801769) and next prime (66801793).
It is a cyclic number.
It is not a de Polignac number, because 66801781 - 219 = 66277493 is a prime.
It is a super-2 number, since 2×668017812 = 8924955889543922, which contains 22 as substring.
It is a Duffinian number.
It is a self number, because there is not a number n which added to its sum of digits gives 66801781.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (66201781) by changing a digit.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8865 + ... + 14566.
It is an arithmetic number, because the mean of its divisors is an integer number (16707016).
Almost surely, 266801781 is an apocalyptic number.
It is an amenable number.
66801781 is a deficient number, since it is larger than the sum of its proper divisors (26283).
66801781 is a wasteful number, since it uses less digits than its factorization.
66801781 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 26282.
The product of its (nonzero) digits is 16128, while the sum is 37.
The square root of 66801781 is about 8173.2356505854.
The cubic root of 66801781 is about 405.7538790756.
The spelling of 66801781 in words is "sixty-six million, eight hundred one thousand, seven hundred eighty-one".