781508138 has 4 divisors (see below), whose sum is σ = 1172262210. Its totient is φ = 390754068.

The previous prime is 781508131. The next prime is 781508213. The reversal of 781508138 is 831805187.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 831805187 = 59 ⋅14098393.

It can be written as a sum of positive squares in only one way, i.e., 733163929 + 48344209 = 27077^2 + 6953^2 .

It is a super-2 number, since 2×781508138² = 1221509939520454088, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 781508095 and 781508104.

It is not an unprimeable number, because it can be changed into a prime (781508131) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195377033 + ... + 195377036.

Almost surely, 2^781508138 is an apocalyptic number.

781508138 is a deficient number, since it is larger than the sum of its proper divisors (390754072).

781508138 is a wasteful number, since it uses less digits than its factorization.

781508138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 390754071.

The product of its (nonzero) digits is 53760, while the sum is 41.

The square root of 781508138 is about 27955.4670502927. The cubic root of 781508138 is about 921.1093022656.

The spelling of 781508138 in words is "seven hundred eighty-one million, five hundred eight thousand, one hundred thirty-eight".