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 A089174 Unique prime factors in A007907 extended to modulo 10 (past 20 elements). 0
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. LINKS FORMULA a(n) = If [PrimeQ[IntegerFractors[A007907[m]]]==True, IntegerFractors[A007907[m]]] MATHEMATICA 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] CROSSREFS Cf. A007907. Sequence in context: A332787 A181173 A216277 * A321700 A020636 A141657 Adjacent sequences:  A089171 A089172 A089173 * A089175 A089176 A089177 KEYWORD nonn,base,uned AUTHOR Roger L. Bagula, Dec 07 2003 STATUS approved

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Last modified January 24 22:45 EST 2022. Contains 350565 sequences. (Running on oeis4.)