A134071 Primes in A134072.

31, 431, 117431, 19912376472918117431

Offset: 1

Author

Alexander Adamchuk, Oct 06 2007

Keywords

• hard
• more
• nonn
• base

Comments

A134072 = {1, 31, 431, 7431, 117431, 18117431, 2918117431, 472918117431, 76472918117431, 12376472918117431, 19912376472918117431, ...} = concatenation of Lucas numbers in reverse order. Indices of prime terms in A134072 are {2, 3, 5, 11, ...}.

No further terms through 500 Lucas numbers. - Harvey P. Dale, Aug 17 2013

Examples

			a(1) = A134072(2) = 31.
a(2) = A134072(3) = 431.
a(3) = A134072(5) = 117431.
		

Links

• Eric Weisstein's World of Mathematics, Lucas Number
• Eric Weisstein's World of Mathematics, Smarandache Sequences

Crossrefs

Cf. A000204 (Lucas numbers).

Cf. A130774 (concatenation of Lucas numbers).

Cf. A019523 (concatenation of Fibonacci numbers).

Cf. A038399 (concatenation of first n nonzero Fibonacci numbers in reverse order).

Cf. A134072 (concatenation of A000204 Lucas numbers (beginning at 1) in reverse order).

Cf. A134069 (primes in A038399).

Cf. A134070 (primes in A130774).

Programs

Mathematica

nn=500;With[{lucs=LucasL[Range[nn]]},Select[Table[FromDigits[ Flatten[ IntegerDigits/@ Reverse[ Take[lucs,n]]]],{n,nn}],PrimeQ]] (* Harvey P. Dale, Aug 17 2013 *)

Extensions

Edited by Charles R Greathouse IV, Apr 24 2010