21028973557 has 2 divisors, whose sum is σ = 21028973558. Its totient is φ = 21028973556.

The previous prime is 21028973533. The next prime is 21028973561. The reversal of 21028973557 is 75537982012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11407521636 + 9621451921 = 106806^2 + 98089^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21028973557 is a prime.

It is a super-2 number, since 2×21028973557² (a number of 21 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 21028973557.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21028973257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10514486778 + 10514486779.

It is an arithmetic number, because the mean of its divisors is an integer number (10514486779).

Almost surely, 2^21028973557 is an apocalyptic number.

It is an amenable number.

21028973557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21028973557 is an equidigital number, since it uses as much as digits as its factorization.

21028973557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1058400, while the sum is 49.

The spelling of 21028973557 in words is "twenty-one billion, twenty-eight million, nine hundred seventy-three thousand, five hundred fifty-seven".