51664981 has 2 divisors, whose sum is σ = 51664982. Its totient is φ = 51664980.

The previous prime is 51664939. The next prime is 51664993. The reversal of 51664981 is 18946615.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 33466225 + 18198756 = 5785^2 + 4266^2 .

It is a cyclic number.

It is not a de Polignac number, because 51664981 - 2²⁵ = 18110549 is a prime.

It is a super-2 number, since 2×51664981² = 5338540523460722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51664931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25832490 + 25832491.

It is an arithmetic number, because the mean of its divisors is an integer number (25832491).

Almost surely, 2^51664981 is an apocalyptic number.

It is an amenable number.

51664981 is a deficient number, since it is larger than the sum of its proper divisors (1).

51664981 is an equidigital number, since it uses as much as digits as its factorization.

51664981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 51840, while the sum is 40.

The square root of 51664981 is about 7187.8356269464. The cubic root of 51664981 is about 372.4478097534.

The spelling of 51664981 in words is "fifty-one million, six hundred sixty-four thousand, nine hundred eighty-one".