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A089690 a={1,3,7,9} a1={1,3,7,9,0} b[n]=Flatten[Table[10*Sum[10^m*a1[[1+Mod[n,5]]],{m,0,n}]+a,{n,0,digits}]]; a[m]=if b[n] is prime then b[n] 0
3, 7, 11, 13, 17, 19, 331, 337, 99991, 33333331, 777777773, 11111111111111119, 333333333333333331, 999999999999999999999999999999999999999999991, 333333333333333333333333333333333333333333333333333333333333333333333333333331 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A strange set of primes from a prime generator function experiment.

The digit repeatings in these numbers which are primes make them interesting. It doesn't seem like they should be primes.

LINKS

Table of n, a(n) for n=1..15.

MATHEMATICA

a={1, 3, 7, 9} a1={1, 3, 7, 9, 0} digits=100 b=Flatten[Table[10*Sum[10^m*a1[[1+Mod[n, 5]]], {m, 0, n}]+a, {n, 0, digits}]]; c=Table[If[PrimeQ[b[[n]]]==True, b[[n]], 0], {n, 1, Dimensions[b][[1]]}] d=Delete[Union[c], 1]

CROSSREFS

Sequence in context: A091633 A166559 A177193 * A310194 A310195 A310196

Adjacent sequences:  A089687 A089688 A089689 * A089691 A089692 A089693

KEYWORD

nonn,base,less

AUTHOR

Roger L. Bagula, Jan 05 2004

STATUS

approved

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Last modified October 17 08:36 EDT 2019. Contains 328107 sequences. (Running on oeis4.)