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A058036
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Smallest primitive prime factor of the n-th Lucas number (A000032); i.e., L(n), L(0) = 2, L(1) = 1 and L(n) = L(n-1) + L(n-2).
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6
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2, 1, 3, 1, 7, 11, 1, 29, 47, 19, 41, 199, 23, 521, 281, 31, 2207, 3571, 107, 9349, 2161, 211, 43, 139, 1103, 101, 90481, 5779, 14503, 59, 2521, 3010349, 1087, 9901, 67, 71, 103681, 54018521, 29134601, 79, 1601, 370248451, 83, 6709, 263, 181, 4969
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OFFSET
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0,1
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COMMENTS
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A Lucas number can have more than one primitive factor; the primitive factors of L(22) are 43 and 307.
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LINKS
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MATHEMATICA
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a=3; b=-1; prms={}; Table[c=a+b; a=b; b=c; f=First/@FactorInteger[c]; p=Complement[f, prms]; prms=Join[prms, p]; If[p=={}, 1, First[p]], {47}]
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PROG
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(PARI) lucas(n) = fibonacci(n+1)+fibonacci(n-1); \\ A000032
a(n) = {n++; my(v = vector(n, k, k--; lucas(k))); my(vf = vector(n, k, factor(v[k])[, 1]~)); for (k=1, n-1, vf[n] = setminus(vf[n], vf[k]); ); if (#vf[n], vecmin(vf[n]), 1); } \\ Michel Marcus, May 11 2021
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CROSSREFS
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Cf. A001578 (analog for Fibonacci).
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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