1261637911657 has 2 divisors, whose sum is σ = 1261637911658. Its totient is φ = 1261637911656.

The previous prime is 1261637911649. The next prime is 1261637911691. The reversal of 1261637911657 is 7561197361621.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 932700103696 + 328937807961 = 965764^2 + 573531^2 .

It is a cyclic number.

It is not a de Polignac number, because 1261637911657 - 2³ = 1261637911649 is a prime.

It is a super-2 number, since 2×1261637911657² (a number of 25 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 1261637911598 and 1261637911607.

It is not a weakly prime, because it can be changed into another prime (1261637921657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 630818955828 + 630818955829.

It is an arithmetic number, because the mean of its divisors is an integer number (630818955829).

Almost surely, 2^{1261637911657} is an apocalyptic number.

It is an amenable number.

1261637911657 is a deficient number, since it is larger than the sum of its proper divisors (1).

1261637911657 is an equidigital number, since it uses as much as digits as its factorization.

1261637911657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2857680, while the sum is 55.

The spelling of 1261637911657 in words is "one trillion, two hundred sixty-one billion, six hundred thirty-seven million, nine hundred eleven thousand, six hundred fifty-seven".