A034969 a(1) = a(2) = 1, a(n) is largest prime factor of concatenation of a(n - 2) and a(n - 1).

1, 1, 11, 37, 379, 37379, 130369, 463, 12277, 4210207, 1015309, 42102071015309, 7522851571, 39903394005601130021, 747580650949733, 2601211879473948668292638737, 16287160151410310678021523908384898241043, 37391601140774556436246253

Offset: 1

Author

Erich Friedman

Keywords

• nonn
• base
• nice

Examples

			a(6) = 37379 because the concatenation of a(4) and a(5) is 37379, a prime number.
a(7) = 130369 because the concatenation of a(5) and a(6) is 37937379 = 3 * 97 * 130369.
		

Links

• Sean A. Irvine, Table of n, a(n) for n = 1..26

Programs

Mathematica

nxt[{a_,b_}]:={b,FactorInteger[FromDigits[Flatten[IntegerDigits[ {a,b}]]]][[-1,1]]}; Transpose[NestList[nxt,{1,1},18]][[1]] (* Harvey P. Dale, Nov 24 2012 *)

Extensions

Corrected and extended by Harvey P. Dale, Nov 24 2012