648777781 has 4 divisors (see below), whose sum is σ = 682924000. Its totient is φ = 614631564.

The previous prime is 648777757. The next prime is 648777793. The reversal of 648777781 is 187777846.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 648777781 - 2²³ = 640389173 is a prime.

It is a super-2 number, since 2×648777781² = 841825218238567922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (648777751) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17073081 + ... + 17073118.

It is an arithmetic number, because the mean of its divisors is an integer number (170731000).

Almost surely, 2^648777781 is an apocalyptic number.

It is an amenable number.

648777781 is a deficient number, since it is larger than the sum of its proper divisors (34146219).

648777781 is a wasteful number, since it uses less digits than its factorization.

648777781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34146218.

The product of its digits is 3687936, while the sum is 55.

The square root of 648777781 is about 25471.1166029289. The cubic root of 648777781 is about 865.6958242233.

The spelling of 648777781 in words is "six hundred forty-eight million, seven hundred seventy-seven thousand, seven hundred eighty-one".