a²+1是素数，素数大于5的都是奇数，
a²+1是奇数，a是偶数，a的个位是2或8时m的个位是5是合数，a的个位是4或6时m的个位是7，a个位数只能是0，m的个位是1，然后就找（10a）²+1是素数的数。

还可能是1呀，a=10时a²+1=101是素数

2024-06-05 09:30:12
a = 1, (10a)^2 + 1 is prime
a = 2, (10a)^2 + 1 is prime
a = 4, (10a)^2 + 1 is prime
a = 9, (10a)^2 + 1 is prime
a = 11, (10a)^2 + 1 is prime
a = 12, (10a)^2 + 1 is prime
a = 13, (10a)^2 + 1 is prime
a = 15, (10a)^2 + 1 is prime
a = 16, (10a)^2 + 1 is prime
a = 17, (10a)^2 + 1 is prime
a = 18, (10a)^2 + 1 is prime
a = 21, (10a)^2 + 1 is prime
a = 23, (10a)^2 + 1 is prime
a = 24, (10a)^2 + 1 is prime
a = 25, (10a)^2 + 1 is prime
a = 26, (10a)^2 + 1 is prime
a = 27, (10a)^2 + 1 is prime
a = 28, (10a)^2 + 1 is prime
a = 30, (10a)^2 + 1 is prime
a = 34, (10a)^2 + 1 is prime
a = 35, (10a)^2 + 1 is prime
a = 40, (10a)^2 + 1 is prime
a = 42, (10a)^2 + 1 is prime
a = 43, (10a)^2 + 1 is prime
a = 44, (10a)^2 + 1 is prime
a = 47, (10a)^2 + 1 is prime
a = 49, (10a)^2 + 1 is prime
a = 57, (10a)^2 + 1 is prime
a = 68, (10a)^2 + 1 is prime
a = 69, (10a)^2 + 1 is prime
a = 70, (10a)^2 + 1 is prime
a = 74, (10a)^2 + 1 is prime
a = 75, (10a)^2 + 1 is prime
a = 76, (10a)^2 + 1 is prime
a = 78, (10a)^2 + 1 is prime
a = 86, (10a)^2 + 1 is prime
a = 89, (10a)^2 + 1 is prime
a = 91, (10a)^2 + 1 is prime
a = 92, (10a)^2 + 1 is prime
a = 93, (10a)^2 + 1 is prime
a = 95, (10a)^2 + 1 is prime
a = 96, (10a)^2 + 1 is prime
用时 0.000000 秒

疏忽了，只算个位是1，2，3→9的情况，忘记了还有0。所以排除a被10整除的就好了。

a^2+1个位数为，0,1,2,5,6,7，1和7都有可能是素数