64821781 has 2 divisors, whose sum is σ = 64821782. Its totient is φ = 64821780.

The previous prime is 64821767. The next prime is 64821821. The reversal of 64821781 is 18712846.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 38862756 + 25959025 = 6234^2 + 5095^2 .

It is a cyclic number.

It is not a de Polignac number, because 64821781 - 2¹⁷ = 64690709 is a prime.

It is a super-2 number, since 2×64821781² = 8403726584023922, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 64821781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (64821721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 32410890 + 32410891.

It is an arithmetic number, because the mean of its divisors is an integer number (32410891).

Almost surely, 2^64821781 is an apocalyptic number.

It is an amenable number.

64821781 is a deficient number, since it is larger than the sum of its proper divisors (1).

64821781 is an equidigital number, since it uses as much as digits as its factorization.

64821781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21504, while the sum is 37.

The square root of 64821781 is about 8051.1974885727. The cubic root of 64821781 is about 401.7047678447.

The spelling of 64821781 in words is "sixty-four million, eight hundred twenty-one thousand, seven hundred eighty-one".