A258217 Smallest multiple of 7 starting with n, that did not appear earlier.

14, 21, 35, 42, 56, 63, 7, 84, 91, 105, 112, 126, 133, 140, 154, 161, 175, 182, 196, 203, 210, 224, 231, 245, 252, 266, 273, 28, 294, 301, 315, 322, 336, 343, 350, 364, 371, 385, 392, 406, 413, 420, 434, 441, 455, 462, 476, 483, 49, 504, 511, 525, 532, 546

Offset: 1

Author

Eric Angelini and Reinhard Zumkeller, May 23 2015

Keywords

• nonn
• base

Comments

The sequence is a permutation of the positive multiples of 7. - Vladimir Shevelev, May 24 2015

A258334(n) = a(n) / 7 is a permutation of the positive integers. - Reinhard Zumkeller, May 27 2015

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Éric Angelini, Multiples of 3 ending with n, SeqFan list, May 23 2015.

Crossrefs

Cf. A008589, A258188, A258083, A258334.

Programs

Haskell

import Data.List (isPrefixOf, delete)
a258217 n = a258217_list !! (n-1)
a258217_list = f 1 $ tail $ zip a008589_list $ map show a008589_list where
   f x ws = g ws where
     g ((u, vs) : uvs) = if isPrefixOf (show x) vs
                         then u : f (x + 1) (delete (u, vs) ws) else g uvs

Mathematica

a[1] = 14; a[n_] := a[n] = For[dn = IntegerDigits[n]; k = 7, True, k = k+7, dk = IntegerDigits[k]; lg = Min[Length[dn], Length[dk]]; If[Union[ Take[dk, lg] - Take[dn, lg]] == {0} && FreeQ[Array[a, n-1], k], Return[k]]]; Array[a, 54] (* Jean-François Alcover, Feb 09 2018 *)