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A089174
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Unique prime factors in A007907 extended to modulo 10 (past 20 elements).
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0
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2, 3, 7, 11, 13, 17, 19, 23, 37, 41, 59, 73, 101, 137, 157, 239, 257, 271, 547, 2153, 2251, 4649, 7309, 9091, 19697, 21683, 94331, 333667, 928163, 3324301, 4403881, 7532639, 8983031, 10901027, 1111211111, 11195538763, 139381546141, 1102732004467
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OFFSET
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1,1
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COMMENTS
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Set contains two primes that are also palindromic: {11,123456789012343210987654321} Other prime factors might exist if the set were extended past n=30, but the factoring problem doesn't stop on my computer at n=50. A007907 as presented in the database is a limited set of palindromes of the digit set {1,2,3,4,5,6,7,8,9} . My modulo ten version extends the set by adding zero to the digit set.
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LINKS
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Table of n, a(n) for n=1..38.
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FORMULA
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a(n) = If [PrimeQ[IntegerFractors[A007907[m]]]==True, IntegerFractors[A007907[m]]]
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MATHEMATICA
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digits=30 (* general palindromic 0, 1, 2, 3, ..., 9 generator for length m-1*) a[m_]=Delete[Table[If [ Floor[m/2]-n>=0, Mod[ n, 10], Mod[m-n, 10]], {n, 1, m}], m] b=Table[Sum[a[m][[i]]*10^(i-1), {i, 1, m-1}], {m, 2, digits}] c=Flatten[Table[FactorInteger[b[[n]]], {n, 1, digits-1}]] d=Delete[Union[ Table[If[PrimeQ[c[[n]]]==True, c[[n]], 1], {n, 1, Dimensions[c][[1]]}]], 1]
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CROSSREFS
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Cf. A007907.
Sequence in context: A086339 A181173 A216277 * A020636 A141657 A071200
Adjacent sequences: A089171 A089172 A089173 * A089175 A089176 A089177
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KEYWORD
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nonn,base,uned,changed
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AUTHOR
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Roger L. Bagula, Dec 07 2003
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STATUS
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approved
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