7978 has 4 divisors (see below), whose sum is σ = 11970. Its totient is φ = 3988.
The previous prime is 7963. The next prime is 7993. The reversal of 7978 is 8797.
It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 8797 = 19 ⋅463.
It is an interprime number because it is at equal distance from previous prime (7963) and next prime (7993).
It can be written as a sum of positive squares in only one way, i.e., 6889 + 1089 = 83^2 + 33^2 .
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 a plaindrome in base 15.
It is an unprimeable number.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1993 + ... + 1996.
27978 is an apocalyptic number.
7978 is a deficient number, since it is larger than the sum of its proper divisors (3992).
7978 is a wasteful number, since it uses less digits than its factorization.
7978 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 3991.
The product of its digits is 3528, while the sum is 31.
The square root of 7978 is about 89.3196506935. The cubic root of 7978 is about 19.9816498354.
The spelling of 7978 in words is "seven thousand, nine hundred seventy-eight".
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