21661453149517 has 2 divisors, whose sum is σ = 21661453149518. Its totient is φ = 21661453149516.

The previous prime is 21661453149491. The next prime is 21661453149569. The reversal of 21661453149517 is 71594135416612.

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., 18431403098761 + 3230050050756 = 4293181^2 + 1797234^2 .

It is a cyclic number.

It is not a de Polignac number, because 21661453149517 - 2¹¹ = 21661453147469 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21661453549517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10830726574758 + 10830726574759.

It is an arithmetic number, because the mean of its divisors is an integer number (10830726574759).

Almost surely, 2^{21661453149517} is an apocalyptic number.

It is an amenable number.

21661453149517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21661453149517 is an equidigital number, since it uses as much as digits as its factorization.

21661453149517 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5443200, while the sum is 55.

The spelling of 21661453149517 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred fifty-three million, one hundred forty-nine thousand, five hundred seventeen".