256781621 has 2 divisors, whose sum is σ = 256781622. Its totient is φ = 256781620.

The previous prime is 256781597. The next prime is 256781641. The reversal of 256781621 is 126187652.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 156000100 + 100781521 = 12490^2 + 10039^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-256781621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (256781641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 128390810 + 128390811.

It is an arithmetic number, because the mean of its divisors is an integer number (128390811).

Almost surely, 2^256781621 is an apocalyptic number.

It is an amenable number.

256781621 is a deficient number, since it is larger than the sum of its proper divisors (1).

256781621 is an equidigital number, since it uses as much as digits as its factorization.

256781621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 40320, while the sum is 38.

The square root of 256781621 is about 16024.4070405117. The cubic root of 256781621 is about 635.6059860913.

The spelling of 256781621 in words is "two hundred fifty-six million, seven hundred eighty-one thousand, six hundred twenty-one".