781721028 has 144 divisors (see below), whose sum is σ = 2292675840. Its totient is φ = 222091200.

The previous prime is 781721027. The next prime is 781721051. The reversal of 781721028 is 820127187.

It is a happy number.

It is a super-2 number, since 2×781721028² = 1222175531234753568, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 781720983 and 781721001.

It is not an unprimeable number, because it can be changed into a prime (781721021) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 804583 + ... + 805553.

It is an arithmetic number, because the mean of its divisors is an integer number (15921360).

Almost surely, 2^781721028 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 781721028, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1146337920).

781721028 is an abundant number, since it is smaller than the sum of its proper divisors (1510954812).

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

781721028 is a wasteful number, since it uses less digits than its factorization.

781721028 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1118 (or 1113 counting only the distinct ones).

The product of its (nonzero) digits is 12544, while the sum is 36.

The square root of 781721028 is about 27959.2744541056. The cubic root of 781721028 is about 921.1929342188.

The spelling of 781721028 in words is "seven hundred eighty-one million, seven hundred twenty-one thousand, twenty-eight".