70991981 has 4 divisors (see below), whose sum is σ = 71128764. Its totient is φ = 70855200.

The previous prime is 70991969. The next prime is 70991993. The reversal of 70991981 is 18919907.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (70991969) and next prime (70991993).

It can be written as a sum of positive squares in 2 ways, for example, as 52852900 + 18139081 = 7270^2 + 4259^2 .

It is a cyclic number.

It is not a de Polignac number, because 70991981 - 2¹⁰ = 70990957 is a prime.

It is a super-2 number, since 2×70991981² = 10079722732608722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (70991941) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 67610 + ... + 68651.

It is an arithmetic number, because the mean of its divisors is an integer number (17782191).

Almost surely, 2^70991981 is an apocalyptic number.

It is an amenable number.

70991981 is a deficient number, since it is larger than the sum of its proper divisors (136783).

70991981 is a wasteful number, since it uses less digits than its factorization.

70991981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 136782.

The product of its (nonzero) digits is 40824, while the sum is 44.

The square root of 70991981 is about 8425.6739196340. The cubic root of 70991981 is about 414.0661850513.

The spelling of 70991981 in words is "seventy million, nine hundred ninety-one thousand, nine hundred eighty-one".