A052080 Concatenation of n consecutive descending numbers starting from a(n) produces the smallest possible prime of this form, 0 if no such prime exists.

2, 4, 0, 10, 7, 0, 73, 46, 0, 56, 219, 0, 25, 60, 0, 52, 117, 0, 535, 172, 0

Offset: 1

Author

Patrick De Geest, Jan 15 2000

Keywords

• nonn
• base
• hard

Comments

First hard cases occur for n = 22, 88 and 110.

a(22) = 10^1631 + 10 was found by James G. Merickel in Feb 2011.

a(88) = 10^14 + 6.

a(110) = 10^19 + 26 was found by Chris Nash.

Examples

			For n = 8 we have a(8) = 46 so the eight consecutive descending numbers 46,45,44,43,42,41,40 and 39 concatenated together gives the smallest possible prime of this form, 4645444342414039.
		

Links

• C. Rivera, Prime Puzzle 78

Crossrefs

Cf. A052077, A052078, A052079.

Extensions

Terms a(7)-a(21) calculated by Carlos Rivera and Felice Russo