21661457343881 has 2 divisors, whose sum is σ = 21661457343882. Its totient is φ = 21661457343880.

The previous prime is 21661457343821. The next prime is 21661457343913. The reversal of 21661457343881 is 18834375416612.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21578031686656 + 83425657225 = 4645216^2 + 288835^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21661457343881 is a prime.

It is a super-2 number, since 2×21661457343881² (a number of 27 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21661457343881.

It is not a weakly prime, because it can be changed into another prime (21661457343821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830728671940 + 10830728671941.

It is an arithmetic number, because the mean of its divisors is an integer number (10830728671941).

Almost surely, 2^{21661457343881} is an apocalyptic number.

It is an amenable number.

21661457343881 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661457343881 is an equidigital number, since it uses as much as digits as its factorization.

21661457343881 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23224320, while the sum is 59.

The spelling of 21661457343881 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred fifty-seven million, three hundred forty-three thousand, eight hundred eighty-one".