66813521 has 2 divisors, whose sum is σ = 66813522. Its totient is φ = 66813520.

The previous prime is 66813499. The next prime is 66813533. The reversal of 66813521 is 12531866.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66601921 + 211600 = 8161^2 + 460^2 .

It is a cyclic number.

It is not a de Polignac number, because 66813521 - 2¹⁸ = 66551377 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (66813541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33406760 + 33406761.

It is an arithmetic number, because the mean of its divisors is an integer number (33406761).

Almost surely, 2^66813521 is an apocalyptic number.

It is an amenable number.

66813521 is a deficient number, since it is larger than the sum of its proper divisors (1).

66813521 is an equidigital number, since it uses as much as digits as its factorization.

66813521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 32.

The square root of 66813521 is about 8173.9538168502. The cubic root of 66813521 is about 405.7776472619. Note that the first 3 decimals are identical.

The spelling of 66813521 in words is "sixty-six million, eight hundred thirteen thousand, five hundred twenty-one".