66261521 has 2 divisors, whose sum is σ = 66261522. Its totient is φ = 66261520.

The previous prime is 66261511. The next prime is 66261523. The reversal of 66261521 is 12516266.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 59830225 + 6431296 = 7735^2 + 2536^2 .

It is a cyclic number.

It is not a de Polignac number, because 66261521 - 2⁶ = 66261457 is a prime.

Together with 66261523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (66261523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33130760 + 33130761.

It is an arithmetic number, because the mean of its divisors is an integer number (33130761).

Almost surely, 2^66261521 is an apocalyptic number.

It is an amenable number.

66261521 is a deficient number, since it is larger than the sum of its proper divisors (1).

66261521 is an equidigital number, since it uses as much as digits as its factorization.

66261521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 29.

The square root of 66261521 is about 8140.1179966878. The cubic root of 66261521 is about 404.6570708853.

Adding to 66261521 its reverse (12516266), we get a palindrome (78777787).

The spelling of 66261521 in words is "sixty-six million, two hundred sixty-one thousand, five hundred twenty-one".