64671781 has 2 divisors, whose sum is σ = 64671782. Its totient is φ = 64671780.

The previous prime is 64671767. The next prime is 64671787. The reversal of 64671781 is 18717646.

64671781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 34035556 + 30636225 = 5834^2 + 5535^2 .

It is a cyclic number.

It is not a de Polignac number, because 64671781 - 2¹¹ = 64669733 is a prime.

It is a super-2 number, since 2×64671781² = 8364878515423922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (64671787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 32335890 + 32335891.

It is an arithmetic number, because the mean of its divisors is an integer number (32335891).

Almost surely, 2^64671781 is an apocalyptic number.

It is an amenable number.

64671781 is a deficient number, since it is larger than the sum of its proper divisors (1).

64671781 is an equidigital number, since it uses as much as digits as its factorization.

64671781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 56448, while the sum is 40.

The square root of 64671781 is about 8041.8767088286. The cubic root of 64671781 is about 401.3946753003.

It can be divided in two parts, 646 and 71781, that added together give a palindrome (72427).

The spelling of 64671781 in words is "sixty-four million, six hundred seventy-one thousand, seven hundred eighty-one".