21130501661 has 2 divisors, whose sum is σ = 21130501662. Its totient is φ = 21130501660.

The previous prime is 21130501633. The next prime is 21130501729. The reversal of 21130501661 is 16610503112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12722712025 + 8407789636 = 112795^2 + 91694^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21130501661 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21130501661.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21130501261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10565250830 + 10565250831.

It is an arithmetic number, because the mean of its divisors is an integer number (10565250831).

Almost surely, 2^21130501661 is an apocalyptic number.

It is an amenable number.

21130501661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21130501661 is an equidigital number, since it uses as much as digits as its factorization.

21130501661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1080, while the sum is 26.

The spelling of 21130501661 in words is "twenty-one billion, one hundred thirty million, five hundred one thousand, six hundred sixty-one".