A281002 Square array read by antidiagonals downwards: A(n, 1) = second Wieferich prime to base n and A(n, k) = second Wieferich prime to base A(n, k-1) for k > 1.

3511, 19, 1006003, 7, 11, 3511, 491531

Offset: 2

Author

Felix Fröhlich, Jan 12 2017

Keywords

• nonn
• tabl
• more

Examples

			Array starts:
     3511,    19,     7, 491531, ...
  1006003,    11, ...
     3511,    19,     7, 491531, ...
    20771, 18043, ...
   534851,     5, 20771,  18043, ...
		

Crossrefs

Cf. A178871, A281001.

Programs

PARI

secondwieftobase(n) = my(i=0); forprime(p=1, , if(Mod(n, p^2)^(p-1)==1, if(i==0, i++, return(p))))
table(rows, cols) = for(x=2, rows+1, my(i=0, w=secondwieftobase(x)); while(i < cols, print1(w, ", "); w=secondwieftobase(w); i++); print(""))
table(2, 3)