64557781 has 2 divisors, whose sum is σ = 64557782. Its totient is φ = 64557780.

The previous prime is 64557761. The next prime is 64557791. The reversal of 64557781 is 18775546.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 61371556 + 3186225 = 7834^2 + 1785^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-64557781 is a prime.

It is a super-2 number, since 2×64557781² = 8335414175287922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (64557751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 32278890 + 32278891.

It is an arithmetic number, because the mean of its divisors is an integer number (32278891).

Almost surely, 2^64557781 is an apocalyptic number.

It is an amenable number.

64557781 is a deficient number, since it is larger than the sum of its proper divisors (1).

64557781 is an equidigital number, since it uses as much as digits as its factorization.

64557781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 235200, while the sum is 43.

The square root of 64557781 is about 8034.7856847585. The cubic root of 64557781 is about 401.1586841369.

The spelling of 64557781 in words is "sixty-four million, five hundred fifty-seven thousand, seven hundred eighty-one".