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 A072957 Urban numbers: without 'r' or 'u'. 4

%I

%S 1,2,5,6,7,8,9,10,11,12,15,16,17,18,19,20,21,22,25,26,27,28,29,50,51,

%T 55,56,57,58,59,60,61,62,65,66,67,68,69,70,71,72,75,76,77,78,79,80,81,

%U 82,85,86,87,88,89,90,91,92,95,96,97,98,99,1000000,1000001,1000002

%N Urban numbers: without 'r' or 'u'.

%D M. J. Halm, Sequences (Re)discovered, Mpossibilities 81 (Aug. 2002).

%o (PARI) is(n)=!setintersect(Set(Vec(English(n))),["r","u"]) \\ See A052360 for English(). - _M. F. Hasler_, Apr 01 2019

%o /* Alternate code, not using English(): (valid for 1 <= n < one trillion, which should be forbidden due to the 'r' but returns 1) */

%o is(n)={setintersect( Set(digits(n)), [3,4]) && return; !while(n=divrem(n,10^6), n[2]<100||return; n=n[1])} \\ _M. F. Hasler_, Apr 01 2019

%Y Cf. A006933 (eban numbers: without 'e'), A008521 (without 'o'), A008523 (without 't'), A008537 (without 'n'), A089590 (without 'u'), A072956 (turban numbers: without r, t or u), A089589 (without 'i').

%K easy,nonn,word

%O 1,2

%A _Michael Joseph Halm_, Aug 13 2002

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Last modified September 15 20:42 EDT 2019. Contains 327087 sequences. (Running on oeis4.)