781649820 has 144 divisors (see below), whose sum is σ = 2729825280. Its totient is φ = 177337728.

The previous prime is 781649819. The next prime is 781649833. The reversal of 781649820 is 28946187.

It is a super-2 number, since 2×781649820² = 1221952882212064800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 172909 + ... + 177371.

It is an arithmetic number, because the mean of its divisors is an integer number (18957120).

Almost surely, 2^781649820 is an apocalyptic number.

781649820 is a gapful number since it is divisible by the number (70) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 781649820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1364912640).

781649820 is an abundant number, since it is smaller than the sum of its proper divisors (1948175460).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

781649820 is a wasteful number, since it uses less digits than its factorization.

781649820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4624 (or 4619 counting only the distinct ones).

The product of its (nonzero) digits is 193536, while the sum is 45.

The square root of 781649820 is about 27958.0010015022. The cubic root of 781649820 is about 921.1649624761.

The spelling of 781649820 in words is "seven hundred eighty-one million, six hundred forty-nine thousand, eight hundred twenty".