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A066811 Numbers k such that the concatenation of odd numbers from 1 to k is a prime. 3
3, 19, 31, 67, 97, 5139 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..6.

FORMULA

a(n) = 2*A046036(n) - 1. - Michel Marcus, Jan 31 2014

EXAMPLE

E.g., 19 is a term because 135791113151719 is a prime.

MATHEMATICA

p = ""; Do[p = p <> ToString[2*n+1]; If[PrimeQ[ToExpression[p]], Print[2*n+1]], {n, 0, 2569}] (* Ryan Propper, Aug 26 2005 *)

CROSSREFS

Cf. A000040, A005408, A048847.

Sequence in context: A236969 A222590 A107165 * A269414 A162307 A128069

Adjacent sequences:  A066808 A066809 A066810 * A066812 A066813 A066814

KEYWORD

base,nonn

AUTHOR

Patrick De Geest, Jan 20 2002

EXTENSIONS

5139 from Ryan Propper, Aug 26 2005

STATUS

approved

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Last modified April 23 03:26 EDT 2019. Contains 322380 sequences. (Running on oeis4.)