81556445261 has 2 divisors, whose sum is σ = 81556445262. Its totient is φ = 81556445260.

The previous prime is 81556445239. The next prime is 81556445309. The reversal of 81556445261 is 16254465518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 67220932900 + 14335512361 = 259270^2 + 119731^2 .

It is a cyclic number.

It is not a de Polignac number, because 81556445261 - 2¹⁰ = 81556444237 is a prime.

It is a super-3 number, since 3×81556445261³ (a number of 34 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81556445161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40778222630 + 40778222631.

It is an arithmetic number, because the mean of its divisors is an integer number (40778222631).

Almost surely, 2^81556445261 is an apocalyptic number.

It is an amenable number.

81556445261 is a deficient number, since it is larger than the sum of its proper divisors (1).

81556445261 is an equidigital number, since it uses as much as digits as its factorization.

81556445261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1152000, while the sum is 47.

The spelling of 81556445261 in words is "eighty-one billion, five hundred fifty-six million, four hundred forty-five thousand, two hundred sixty-one".