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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. 3
2, 4, 0, 10, 7, 0, 73, 46, 0, 56, 219, 0, 25, 60, 0, 52, 117, 0, 535, 172, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

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.

LINKS

Table of n, a(n) for n=1..21.

C. Rivera, Prime Puzzle 78

EXAMPLE

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.

CROSSREFS

Cf. A052077, A052078, A052079.

Sequence in context: A021419 A180192 A066529 * A261754 A073451 A078022

Adjacent sequences:  A052077 A052078 A052079 * A052081 A052082 A052083

KEYWORD

nonn,base,hard

AUTHOR

Patrick De Geest, Jan 15 2000

EXTENSIONS

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

STATUS

approved

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Last modified August 3 05:52 EDT 2020. Contains 336197 sequences. (Running on oeis4.)