1811621781061 has 2 divisors, whose sum is σ = 1811621781062. Its totient is φ = 1811621781060.

The previous prime is 1811621781049. The next prime is 1811621781097. The reversal of 1811621781061 is 1601871261181.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1654246130625 + 157375650436 = 1286175^2 + 396706^2 .

It is a cyclic number.

It is not a de Polignac number, because 1811621781061 - 2⁷ = 1811621780933 is a prime.

It is a super-2 number, since 2×1811621781061² (a number of 25 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 1811621780999 and 1811621781017.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1811621787061) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 905810890530 + 905810890531.

It is an arithmetic number, because the mean of its divisors is an integer number (905810890531).

Almost surely, 2^{1811621781061} is an apocalyptic number.

It is an amenable number.

1811621781061 is a deficient number, since it is larger than the sum of its proper divisors (1).

1811621781061 is an equidigital number, since it uses as much as digits as its factorization.

1811621781061 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32256, while the sum is 43.

The spelling of 1811621781061 in words is "one trillion, eight hundred eleven billion, six hundred twenty-one million, seven hundred eighty-one thousand, sixty-one".