1261802551781 has 2 divisors, whose sum is σ = 1261802551782. Its totient is φ = 1261802551780.

The previous prime is 1261802551663. The next prime is 1261802551787. The reversal of 1261802551781 is 1871552081621.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1106369489281 + 155433062500 = 1051841^2 + 394250^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1261802551781 is a prime.

It is a super-2 number, since 2×1261802551781² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1261802551787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 630901275890 + 630901275891.

It is an arithmetic number, because the mean of its divisors is an integer number (630901275891).

Almost surely, 2^{1261802551781} is an apocalyptic number.

It is an amenable number.

1261802551781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1261802551781 is an equidigital number, since it uses as much as digits as its factorization.

1261802551781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 268800, while the sum is 47.

The spelling of 1261802551781 in words is "one trillion, two hundred sixty-one billion, eight hundred two million, five hundred fifty-one thousand, seven hundred eighty-one".