21505166611651 has 2 divisors, whose sum is σ = 21505166611652. Its totient is φ = 21505166611650.

The previous prime is 21505166611633. The next prime is 21505166611667. The reversal of 21505166611651 is 15611666150512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21505166611651 - 2⁵ = 21505166611619 is a prime.

It is not a weakly prime, because it can be changed into another prime (21505166611051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10752583305825 + 10752583305826.

It is an arithmetic number, because the mean of its divisors is an integer number (10752583305826).

Almost surely, 2^{21505166611651} is an apocalyptic number.

21505166611651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21505166611651 is an equidigital number, since it uses as much as digits as its factorization.

21505166611651 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 324000, while the sum is 46.

The spelling of 21505166611651 in words is "twenty-one trillion, five hundred five billion, one hundred sixty-six million, six hundred eleven thousand, six hundred fifty-one".