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 A258787 Triangle read by rows: T(n, k) = smallest base b > 1 such that p = prime(n) is the k-th base-b Wieferich prime for k = 1, 2, 3, ..., n. 2
 5, 8, 17, 7, 26, 449, 30, 18, 197, 557, 3, 9, 118, 1207, 19601, 22, 146, 19, 361, 8201, 132857, 38, 40, 224, 249, 4625, 296449, 4486949, 54, 28, 68, 99, 4033, 4625, 296449, 126664001, 42, 130, 28, 118, 557, 8201, 997757, 24800401, 2363321449, 14, 41, 374, 1745, 901, 46826, 217682, 9312157, 758427193, 5229752849 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Triangle T(n, k) starts: 5; 8, 17; 7, 26, 449; 30, 18, 197, 557; 3, 9, 118, 1207, 19601; 22, 146, 19, 361, 8201, 132857; 38, 40, 224, 249, 4625, 296449, 4486949; 54, 28, 68, 99, 4033, 4625, 296449, 126664001; 42, 130, 28, 118, 557, 8201, 997757, 24800401, 2363321449; LINKS Table of n, a(n) for n=1..55. EXAMPLE T(4, 3) = 197, because 197 is the smallest base b such that p = prime(4) = 7 is the 3rd base-b Wieferich prime. PROG (PARI) nextwiefbase(n, a) = a++; while(Mod(a, n^2)^(n-1)!=1, a++); a wiefrank(n, a) = i=0; forprime(p=1, n, if(Mod(a, p^2)^(p-1)==1, i++)); i trianglerows(n) = i=1; while(i <= n, p=prime(i); for(k=1, i, b=2; while(wiefrank(p, b)!=k, b=nextwiefbase(p, b)); print1(b, ", ")); print(""); i++) trianglerows(9) \\ print first nine rows of the triangle CROSSREFS Cf. A256236 (diagonal). A286816. Sequence in context: A153363 A154119 A196387 * A185103 A314566 A096545 Adjacent sequences: A258784 A258785 A258786 * A258788 A258789 A258790 KEYWORD nonn,tabl AUTHOR Felix Fröhlich, Jun 10 2015 EXTENSIONS More terms from Max Alekseyev, Oct 14 2023 STATUS approved

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Last modified March 3 04:18 EST 2024. Contains 370499 sequences. (Running on oeis4.)