A081939 a(1) = 2; a(n+1) is the smallest palindrome > a(n) that has a common factor with a(n).
2, 4, 6, 8, 22, 33, 44, 55, 66, 77, 88, 99, 111, 141, 171, 222, 232, 242, 252, 262, 272, 282, 292, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 585, 595, 616, 626, 636, 646, 656, 666, 676, 686, 696, 717, 747, 777, 828, 838, 848, 858, 868, 878, 888, 898
Offset: 1
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Programs
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Maple
dmax:= 5: # to get all terms with at most dmax digits revdigs:= proc(n) local L, Ln, i; L:= convert(n, base, 10); Ln:= nops(L); add(L[i]*10^(Ln-i), i=1..Ln); end proc: P:= $0..9: for d from 2 to dmax do if d::even then P:= P, seq(10^(d/2)*x + revdigs(x), x=10^(d/2-1)..10^(d/2)-1) else m:= (d-1)/2; P:= P, seq(seq(10^(m+1)*x + 10^m*j+revdigs(x), j=0..9),x=10^(m-1)..10^m-1); fi od: P:= [P]: r:= P[3]: Res:= r: count:= 1: for i from 4 to nops(P) do if igcd(P[i],r) > 1 then count:= count+1; r:= P[i]; Res:= Res, r; fi od: Res; # Robert Israel, Jul 04 2018 -
PARI
ispal(n) = my(d=digits(n)); d == Vecrev(d); lista(nn) = {print1(last = 2, ", "); for (n=3, nn, if (ispal(n) && (gcd(n, last) != 1), print1(n, ", "); last = n;););} \\ Michel Marcus, Aug 12 2015
Extensions
More terms from David Wasserman, Jun 29 2004
Comments