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 A166134 a(n+1) is the smallest divisor of a(n)^2+1 that does not yet appear in the sequence, with a(1) = 1. 2
 1, 2, 5, 13, 10, 101, 5101, 26, 677, 45833, 65, 2113, 446477, 130, 16901, 41, 29, 421, 17, 58, 673, 45293, 25, 313, 97, 941, 34057, 50, 61, 1861, 1229, 773, 59753, 89, 34, 1157, 82, 269, 194, 617, 38069, 55740337, 145, 10513, 11052317, 12215371106849 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS All members of the sequence can be represented as the sum of two relatively prime numbers (A008784). It appears that the sequence is infinite and that all such numbers are present. LINKS Ivan Neretin, Table of n, a(n) for n = 1..1000 EXAMPLE After a(4)=13, the divisors of 13^2+1=170 are 1,2, 5, 10, 17, 34, 85, 170. 1, 2, and 5 have already occurred, so a(5) = 10. MATHEMATICA Nest[Append[#, Min[Complement[Divisors[#[[-1]]^2 + 1], #]]] &, {1}, 45] (* Ivan Neretin, Sep 03 2015 *) PROG (PARI) invec(v, x, n)=for(i=1, n, if(v[i]==x, return(1))); 0 bl(n)={local(v, d, ds); v=vector(n, i, 1); for(i=2, n, ds=divisors(v[i-1]^2+1); for(k=2, #ds, d=ds[k]; if(!invec(v, d, i-1), v[i]=d; break))); v} CROSSREFS Cf. A166133, A008784, A031439, A002522. Sequence in context: A241758 A173620 A319920 * A067365 A189993 A112838 Adjacent sequences:  A166131 A166132 A166133 * A166135 A166136 A166137 KEYWORD nonn AUTHOR Franklin T. Adams-Watters, Oct 07 2009 STATUS approved

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Last modified July 23 11:44 EDT 2019. Contains 325254 sequences. (Running on oeis4.)