21505510001 has 2 divisors, whose sum is σ = 21505510002. Its totient is φ = 21505510000.

The previous prime is 21505509973. The next prime is 21505510043. The reversal of 21505510001 is 10001550512.

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., 18110699776 + 3394810225 = 134576^2 + 58265^2 .

It is a cyclic number.

It is not a de Polignac number, because 21505510001 - 2¹⁰ = 21505508977 is a prime.

It is a super-2 number, since 2×21505510001² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21505512001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10752755000 + 10752755001.

It is an arithmetic number, because the mean of its divisors is an integer number (10752755001).

Almost surely, 2^21505510001 is an apocalyptic number.

It is an amenable number.

21505510001 is a deficient number, since it is larger than the sum of its proper divisors (1).

21505510001 is an equidigital number, since it uses as much as digits as its factorization.

21505510001 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 250, while the sum is 20.

The spelling of 21505510001 in words is "twenty-one billion, five hundred five million, five hundred ten thousand, one".