66138521 has 2 divisors, whose sum is σ = 66138522. Its totient is φ = 66138520.

The previous prime is 66138503. The next prime is 66138529. The reversal of 66138521 is 12583166.

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., 62094400 + 4044121 = 7880^2 + 2011^2 .

It is a cyclic number.

It is not a de Polignac number, because 66138521 - 2¹⁴ = 66122137 is a prime.

It is equal to p_3903845 and since 66138521 and 3903845 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (66138529) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33069260 + 33069261.

It is an arithmetic number, because the mean of its divisors is an integer number (33069261).

Almost surely, 2^66138521 is an apocalyptic number.

It is an amenable number.

66138521 is a deficient number, since it is larger than the sum of its proper divisors (1).

66138521 is an equidigital number, since it uses as much as digits as its factorization.

66138521 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 66138521 is about 8132.5593142626. The cubic root of 66138521 is about 404.4065300575.

It can be divided in two parts, 661385 and 21, that multiplied together give a triangular number (13889085 = T₅₂₇₀).

The spelling of 66138521 in words is "sixty-six million, one hundred thirty-eight thousand, five hundred twenty-one".