21651404557 has 2 divisors, whose sum is σ = 21651404558. Its totient is φ = 21651404556.

The previous prime is 21651404519. The next prime is 21651404563. The reversal of 21651404557 is 75540415612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12591981796 + 9059422761 = 112214^2 + 95181^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651404557 - 2⁷ = 21651404429 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21651404597) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10825702278 + 10825702279.

It is an arithmetic number, because the mean of its divisors is an integer number (10825702279).

Almost surely, 2^21651404557 is an apocalyptic number.

It is an amenable number.

21651404557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21651404557 is an equidigital number, since it uses as much as digits as its factorization.

21651404557 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 168000, while the sum is 40.

The spelling of 21651404557 in words is "twenty-one billion, six hundred fifty-one million, four hundred four thousand, five hundred fifty-seven".