781906 has 4 divisors (see below), whose sum is σ = 1172862. Its totient is φ = 390952.

The previous prime is 781897. The next prime is 781919. The reversal of 781906 is 609187.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 609187 = 421 ⋅1447.

It can be written as a sum of positive squares in only one way, i.e., 697225 + 84681 = 835^2 + 291^2 .

It is a super-2 number, since 2×781906² = 1222753985672, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

781906 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195475 + ... + 195478.

2⁷⁸¹⁹⁰⁶ is an apocalyptic number.

781906 is a deficient number, since it is larger than the sum of its proper divisors (390956).

781906 is a wasteful number, since it uses less digits than its factorization.

781906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 390955.

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 781906 is about 884.2544882555. The cubic root of 781906 is about 92.1265586506.

Subtracting from 781906 its sum of digits (31), we obtain a triangular number (781875 = T₁₂₅₀).

The spelling of 781906 in words is "seven hundred eighty-one thousand, nine hundred six".