cp's OEIS Frontend

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.

A190223 Numbers all of whose divisors are numbers whose decimal digits are noncomposite numbers (1,2,3,5,7).

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%I A190223 #24 Sep 14 2020 05:41:56
%S A190223 1,2,3,5,7,11,13,15,17,21,22,23,25,31,33,35,37,51,53,55,71,73,75,77,
%T A190223 111,113,115,121,125,127,131,137,151,155,157,173,175,211,213,217,221,
%U A190223 223,227,231,233,251,253,257,271,275,277,311,313,317,331,337,353
%N A190223 Numbers all of whose divisors are numbers whose decimal digits are noncomposite numbers (1,2,3,5,7).
%C A190223 Subset of A001742.
%C A190223 All terms are obviously odd except for 2 and numbers of the form 2*A004022(k). - _Harvey P. Dale_, May 28 2014 (corrected by _Iain Fox_, Sep 03 2020)
%H A190223 Iain Fox, <a href="/A190223/b190223.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from G. C. Greubel)
%e A190223 Number 115 is in sequence because all divisors of 115 (1, 5, 23, 115) are numbers whose decimal digits are noncomposite numbers (1,2,3,5,7).
%t A190223 ncnQ[n_]:=Module[{digs=Union[Flatten[IntegerDigits/@Divisors[n]]]}, Complement[ digs,{1,2,3,5,7}]=={}]; Select[ Range[ 400],ncnQ] (* _Harvey P. Dale_, May 28 2014 *)
%o A190223 (PARI) is(k) = fordiv(k, d, if(setminus(vecsort(digits(d), , 8), [1, 2, 3, 5, 7]) != [], return(0))); 1 \\ _Iain Fox_, Dec 28 2017
%Y A190223 Supersequence: A001742.
%Y A190223 Cf. A004022, A243534.
%K A190223 nonn,base
%O A190223 1,2
%A A190223 _Jaroslav Krizek_, May 06 2011
%E A190223 More terms from _Harvey P. Dale_, May 28 2014