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 A261171 Value of k for which A260871(n) = A[b](k), with b = A261172(n); A[b](k) = the number whose base-b representation is the concatenation of the base-b representations of (1, ..., k, k-1, ..., 1). 5
 2, 3, 4, 4, 5, 6, 9, 10, 13, 16, 16, 21, 23, 23, 29, 28, 38, 39, 33, 34, 41, 40, 37, 37, 41, 42, 44, 64, 77, 82, 75, 83, 83, 87, 104, 104, 86, 94 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For more data, see the 3rd column of D. Broadhurst's list of [n, b, k, length(A260871(n))] given in A260871. This and the companion sequence A261172 are a compact way of recording the very large primes listed in A260871 by means of the k- and b-value such that A260871(n) = A[A261172(n)](A261171(n)). See A261170 for the number of decimal digits of these primes. - M. F. Hasler, Sep 15 2015 LINKS FORMULA A260871(n) = A[A261172(n)](a(n)), where A[b](k) = Sum_{i=1..#d} d[i]*b^(#d-i), d = concatenation of (1, 2, ..., k, k-1, ..., 1) all written in base b. EXAMPLE A260871(1) = A[2](2), therefore a(1) = 2. A260871(2) = A[3](3), therefore a(2) = 3. A260871(3) = A[2](4), therefore a(3) = 4. PROG (PARI) A261171_list(LIM=1e499)={my(A=List(), p, d); for(b=2, 9e9, for(n=b, 9e9, if(LIMb))); ispseudoprime(p)&&listput(A, [log(p), n]))); apply(t->t[2], vecsort(A))} CROSSREFS Cf. A173427, A260853 - A260859, A173426, A260861 - A260866 and A260860 for A[b] with b=2, ..., b=16 and b=60. See also A260852 = { primes of the form A260851(b) = A[b](b), b in A260343 }. Sequence in context: A015737 A015745 A017854 * A330264 A036416 A084618 Adjacent sequences:  A261168 A261169 A261170 * A261172 A261173 A261174 KEYWORD nonn,base AUTHOR M. F. Hasler, Aug 23 2015 STATUS approved

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Last modified September 21 04:45 EDT 2020. Contains 337266 sequences. (Running on oeis4.)