66213781 has 2 divisors, whose sum is σ = 66213782. Its totient is φ = 66213780.

The previous prime is 66213769. The next prime is 66213809. The reversal of 66213781 is 18731266.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 63520900 + 2692881 = 7970^2 + 1641^2 .

It is a cyclic number.

It is not a de Polignac number, because 66213781 - 2¹⁵ = 66181013 is a prime.

It is a super-2 number, since 2×66213781² = 8768529588631922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66213751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33106890 + 33106891.

It is an arithmetic number, because the mean of its divisors is an integer number (33106891).

Almost surely, 2^66213781 is an apocalyptic number.

It is an amenable number.

66213781 is a deficient number, since it is larger than the sum of its proper divisors (1).

66213781 is an equidigital number, since it uses as much as digits as its factorization.

66213781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12096, while the sum is 34.

The square root of 66213781 is about 8137.1850783917. The cubic root of 66213781 is about 404.5598652994.

The spelling of 66213781 in words is "sixty-six million, two hundred thirteen thousand, seven hundred eighty-one".