This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
a258334 = flip div 7 . a258217
import Data.List (isPrefixOf, delete)
a258083 n = a258083_list !! (n-1)
a258083_list = f 1 $ tail $ zip
a008585_list $ map (reverse . show) a008585_list where
f x ws = g ws where
g ((u, vs) : uvs) = if isPrefixOf xs vs
then u : f (x + 1) (delete (u, vs) ws) else g uvs
xs = reverse $ show x
a[n_] := a[n] = For[k=3, True, k=k+3, If[Divisible[k-n, 10^IntegerLength[n] ] && FreeQ[Array[a, n-1], k], Return[k]]]; Array[a, 56] (* Jean-François Alcover, Feb 06 2018 *)
a(n) = {my(d = digits(n), s = vecsum(d), k); if(s%3 > 0,k = (3 - s%3)%3, i=1; while(i < #d && d[i] == 3,i++); if(i<#d && d[i+1] >= 1 && d[i]-1 == bitand(d[i]-1, 1), k = 3)); k*10^#d + n} \\ David A. Corneth, May 24 2015
import Data.List (isPrefixOf, delete)
a258188 n = a258188_list !! (n-1)
a258188_list = f 1 $ tail $ zip
a008589_list $ map (reverse . show) a008589_list where
f x ws = g ws where
g ((u, vs) : uvs) = if isPrefixOf xs vs
then u : f (x + 1) (delete (u, vs) ws) else g uvs
xs = reverse $ show x
a[n_] := a[n] = For[k = 7, True, k = k + 7, If[Divisible[k - n, 10^IntegerLength[n]] && FreeQ[Array[a, n-1], k], Return[k]]]; Array[a, 54] (* Jean-François Alcover, Feb 07 2018 *)
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