1261556101 has 24 divisors (see below), whose sum is σ = 1414562184. Its totient is φ = 1123799040.

The previous prime is 1261556071. The next prime is 1261556119. The reversal of 1261556101 is 1016551621.

It is a happy number.

It can be written as a sum of positive squares in 12 ways, for example, as 924099201 + 337456900 = 30399^2 + 18370^2 .

It is not a de Polignac number, because 1261556101 - 2¹⁹ = 1261031813 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1261556101.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1261556161) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 671175 + ... + 673051.

It is an arithmetic number, because the mean of its divisors is an integer number (58940091).

Almost surely, 2^1261556101 is an apocalyptic number.

It is an amenable number.

1261556101 is a deficient number, since it is larger than the sum of its proper divisors (153006083).

1261556101 is a wasteful number, since it uses less digits than its factorization.

1261556101 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2041 (or 2028 counting only the distinct ones).

The product of its (nonzero) digits is 1800, while the sum is 28.

The square root of 1261556101 is about 35518.3910249324. The cubic root of 1261556101 is about 1080.5267495048.

It can be divided in two parts, 1261 and 556101, that multiplied together give a square (701243361 = 26481²).

The spelling of 1261556101 in words is "one billion, two hundred sixty-one million, five hundred fifty-six thousand, one hundred one".