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URL: https://oeis.org/A225487

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A225487
Duplicate primes found by Rowland's recurrence in the order of their reappearance.
2
3, 5, 11, 7, 13, 101, 47, 53, 23, 19, 29, 37, 31, 41, 83, 73, 17, 43, 67, 157, 179, 167, 79, 443, 139, 113, 137, 97, 233, 61, 823, 71, 103, 151, 199, 499, 181, 229, 353, 313, 1889, 271, 317, 197, 613, 607, 127, 257, 89, 367, 223, 433, 239, 911, 109, 107, 557
OFFSET
1,1
COMMENTS
Among the first 10^8 terms of A132199 (Rowland's sequence of 1s and primes), 121 terms are prime. Eleven of them appear more than once, and so are a(1), ..., a(11).
Among the first 10^100 terms of A132199 there are 18321 primes; of these, 3074 are distinct and 351 repeated. - Giovanni Resta, Apr 08 2016
See the crossrefs for references, links, and additional comments.
LINKS
EXAMPLE
The first duplicate in Rowland's sequence of primes A137613 = 5, 3, 11, 3, 23, 3, 47, 3, 5, ... is 3, so a(1) = 3. The second duplicate is 5, so a(2) = 5.
MATHEMATICA
t = {}; b1 = 7; Do[b0 = b1; b1 = b0 + GCD[n, b0]; d = b1 - b0; If[d > 1, AppendTo[t, d]], {n, 2, 10^8}]; L = {}; Do[ If[MemberQ[Take[t, n - 1], t[[n]]], AppendTo[L, t[[n]]]], {n, 2, Length[t]}]; DeleteDuplicates[L]
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Sondow, May 08 2013
EXTENSIONS
a(12)-a(57) from Giovanni Resta, Apr 08 2016
STATUS
approved