cp's OEIS Frontend

A342845 Number of distinct even numbers visible as proper substrings of n.

%I A342845 #12 Mar 26 2021 06:32:48
%S A342845 0,0,0,0,0,0,0,0,0,0,1,0,1,0,1,0,1,0,1,0,2,1,1,1,2,1,2,1,2,1,1,0,1,0,
%T A342845 1,0,1,0,1,0,2,1,2,1,1,1,2,1,2,1,1,0,1,0,1,0,1,0,1,0,2,1,2,1,2,1,1,1,
%U A342845 2,1,1,0,1,0,1,0,1,0,1,0,2,1,2,1,2,1,2,1,1,1,1,0,1,0,1,0,1,0,1,0,2,2,3,2,3
%N A342845 Number of distinct even numbers visible as proper substrings of n.
%C A342845 Here substrings must be contiguous.
%H A342845 Reinhard Zumkeller, <a href="/A342845/b342845.txt">Table of n, a(n) for n = 0..10000</a>
%H A342845 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a342/A342845.java">Java program</a> (github)
%e A342845 a(10)=1 because we can form 0.
%e A342845 a(24)=2 because we can form 2, 4.
%e A342845 a(102)=3 because we can form 0, 2, 10.
%e A342845 a(124)=4 because we can form the following even numbers: 2, 4, 12, 24.
%o A342845 (Haskell)
%o A342845 import Data.List (isInfixOf)
%o A342845 a045887 n = length $ filter (`isInfixOf` (show n)) $ map show [0, 2..n-1]
%o A342845 -- Reinhard Zumkeller, Jul 19 2011
%o A342845 (Python)
%o A342845 def a(n):
%o A342845   s, eset = str(n), set()
%o A342845   for i in range(len(s)):
%o A342845     for j in range(i+1, len(s)+1):
%o A342845       if s[j-1] in "02468" and j-i < len(s): # even and proper substring
%o A342845         eset.add(int(s[i:j]))
%o A342845   return len(eset)
%o A342845 print([a(n) for n in range(105)]) # _Michael S. Branicky_, Mar 23 2021
%Y A342845 Cf. A045887, A045888, A342846.
%K A342845 nonn,base,easy
%O A342845 0,21
%A A342845 _Sean A. Irvine_, Mar 24 2021