81779261 has 2 divisors, whose sum is σ = 81779262. Its totient is φ = 81779260.

The previous prime is 81779207. The next prime is 81779263. The reversal of 81779261 is 16297718.

81779261 = 6394² + 6395².

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 40896025 + 40883236 = 6395^2 + 6394^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81779261 is a prime.

It is a super-2 number, since 2×81779261² = 13375695059412242, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 81779263, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81779263) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40889630 + 40889631.

It is an arithmetic number, because the mean of its divisors is an integer number (40889631).

Almost surely, 2^81779261 is an apocalyptic number.

81779261 is the 6395-th centered square number.

It is an amenable number.

81779261 is a deficient number, since it is larger than the sum of its proper divisors (1).

81779261 is an equidigital number, since it uses as much as digits as its factorization.

81779261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 42336, while the sum is 41.

The square root of 81779261 is about 9043.1886522399. The cubic root of 81779261 is about 434.0579622728.

The spelling of 81779261 in words is "eighty-one million, seven hundred seventy-nine thousand, two hundred sixty-one".