66815381 has 4 divisors (see below), whose sum is σ = 70332000. Its totient is φ = 63298764.

The previous prime is 66815347. The next prime is 66815383. The reversal of 66815381 is 18351866.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 66815381 - 2¹⁴ = 66798997 is a prime.

It is a super-2 number, since 2×66815381² = 8928590276350322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66815383) 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, 1758281 + ... + 1758318.

It is an arithmetic number, because the mean of its divisors is an integer number (17583000).

Almost surely, 2^66815381 is an apocalyptic number.

It is an amenable number.

66815381 is a deficient number, since it is larger than the sum of its proper divisors (3516619).

66815381 is a wasteful number, since it uses less digits than its factorization.

66815381 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3516618.

The product of its digits is 34560, while the sum is 38.

The square root of 66815381 is about 8174.0675920866. The cubic root of 66815381 is about 405.7814126645.

The spelling of 66815381 in words is "sixty-six million, eight hundred fifteen thousand, three hundred eighty-one".