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 A260597 Primes as they occur for the first time as factors of terms of A173426 = concatenation(1,2,...,n,n-1,...,1). 1
 11, 3, 37, 101, 41, 271, 7, 13, 239, 4649, 73, 137, 333667, 12345678910987654321, 17636684157301569664903, 2799473675762179389994681, 1109, 4729, 2354041513534224607850261, 571, 3167, 10723, 439781, 2068140300159522133, 75401, 687437, 759077450603 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Or, distinct elements of A260589 in the order they occur for the first time. LINKS M. F. Hasler and Chai Wah Wu, Table of n, a(n) for n = 1..114 (a(n) for n = 1..84 from M. F. Hasler) EXAMPLE A173426(1) = 1;  A173426(2) = 121 = 11^2 => a(1) = 11. A173426(3) = 12321 = 3^2 37^2 => a(2..3) = (3, 37). A173426(4) = 1234321 = 11^2 101^2 => a(4) = 101. A173426(5) = 123454321 = 41^2 271^2 => a(5..6) = (41, 271). A173426(6) = 12345654321 = 3^2 7^2 11^2 13^2 37^2 => a(7..8) = (7, 13). PROG (PARI) S=[]; apply(t->S=setunion(S, t=setminus(Set(t), S)); t, vector(30, n, A260589_row(n))) (Python) from sympy import primefactors A260597_list = [] for n in range(1, 10):     m = primefactors(int(''.join([str(d) for d in range(1, n+1)]+[str(d) for d in range(n-1, 0, -1)])))     for p in m:         if not p in A260597_list: A260597_list.append(p) # Chai Wah Wu, Aug 11 2015 CROSSREFS Sequence in context: A298927 A102380 A204845 * A147555 A157883 A038317 Adjacent sequences:  A260594 A260595 A260596 * A260598 A260599 A260600 KEYWORD nonn AUTHOR M. F. Hasler, Jul 29 2015 STATUS approved

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Last modified January 22 04:27 EST 2020. Contains 331133 sequences. (Running on oeis4.)