66531213 has 24 divisors (see below), whose sum is σ = 113899968. Its totient is φ = 38016864.

The previous prime is 66531197. The next prime is 66531229. The reversal of 66531213 is 31213566.

66531213 is a `hidden beast` number, since 6 + 653 + 1 + 2 + 1 + 3 = 666.

It is an interprime number because it is at equal distance from previous prime (66531197) and next prime (66531229).

It is not a de Polignac number, because 66531213 - 2⁴ = 66531197 is a prime.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66531263) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 17856 + ... + 21257.

It is an arithmetic number, because the mean of its divisors is an integer number (4745832).

Almost surely, 2^66531213 is an apocalyptic number.

66531213 is a gapful number since it is divisible by the number (63) formed by its first and last digit.

It is an amenable number.

66531213 is a deficient number, since it is larger than the sum of its proper divisors (47368755).

66531213 is an equidigital number, since it uses as much as digits as its factorization.

66531213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39135 (or 39123 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 66531213 is about 8156.6667824547. Note that the first 3 decimals coincide. The cubic root of 66531213 is about 405.2053279834.

Adding to 66531213 its reverse (31213566), we get a palindrome (97744779).

It can be divided in two parts, 665 and 31213, that added together give a triangular number (31878 = T₂₅₂).

The spelling of 66531213 in words is "sixty-six million, five hundred thirty-one thousand, two hundred thirteen".