66251021 has 2 divisors, whose sum is σ = 66251022. Its totient is φ = 66251020.

The previous prime is 66250997. The next prime is 66251069. The reversal of 66251021 is 12015266.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50608996 + 15642025 = 7114^2 + 3955^2 .

It is a cyclic number.

It is not a de Polignac number, because 66251021 - 2¹⁸ = 65988877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66251221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33125510 + 33125511.

It is an arithmetic number, because the mean of its divisors is an integer number (33125511).

Almost surely, 2^66251021 is an apocalyptic number.

It is an amenable number.

66251021 is a deficient number, since it is larger than the sum of its proper divisors (1).

66251021 is an equidigital number, since it uses as much as digits as its factorization.

66251021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 66251021 is about 8139.4730173396. The cubic root of 66251021 is about 404.6356953638.

Adding to 66251021 its reverse (12015266), we get a palindrome (78266287).

The spelling of 66251021 in words is "sixty-six million, two hundred fifty-one thousand, twenty-one".