78961981 has 6 divisors (see below), whose sum is σ = 91853790. Its totient is φ = 67681656.

The previous prime is 78961951. The next prime is 78962003. The reversal of 78961981 is 18916987.

It can be written as a sum of positive squares in only one way, i.e., 69039481 + 9922500 = 8309^2 + 3150^2 .

It is a de Polignac number, because none of the positive numbers 2^k-78961981 is a prime.

It is a super-2 number, since 2×78961981² = 12469988886888722, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (49), and also a Moran number because the ratio is a prime number: 1611469 = 78961981 / (7 + 8 + 9 + 6 + 1 + 9 + 8 + 1).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78961931) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 805686 + ... + 805783.

It is an arithmetic number, because the mean of its divisors is an integer number (15308965).

Almost surely, 2^78961981 is an apocalyptic number.

It is an amenable number.

78961981 is a deficient number, since it is larger than the sum of its proper divisors (12891809).

78961981 is a wasteful number, since it uses less digits than its factorization.

78961981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1611483 (or 1611476 counting only the distinct ones).

The product of its digits is 217728, while the sum is 49.

The square root of 78961981 is about 8886.0554240900. The cubic root of 78961981 is about 429.0151989732.

The spelling of 78961981 in words is "seventy-eight million, nine hundred sixty-one thousand, nine hundred eighty-one".