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A053245 Numbers k such that both A053238(k) and A053238(k+1) = 1.

%I A053245 #16 Jun 09 2025 20:26:18
%S A053245 20,49,56,79,108,132,145,170,177,230,253,277,289,307,347,382,405,412,
%T A053245 424,437,495,548,585,592,633,645,704,734,752,764,789,802,841,854,930,
%U A053245 943,967,974,1005,1012,1053,1066,1130,1154,1179,1186,1216,1223,1264
%N A053245 Numbers k such that both A053238(k) and A053238(k+1) = 1.
%C A053245 Pairs of consecutive 1's occur uncommonly often in A053238.
%H A053245 Reinhard Zumkeller, <a href="/A053245/b053245.txt">Table of n, a(n) for n = 1..10000</a>
%p A053245 with(numtheory): f := [seq( `if`((sigma(i) > sigma(i+1)),i,print( )), i=1..5000)];
%p A053245 seq(`if`((f[i+2]-f[i+1]=1) and (f[i+1]-f[i]=1),i,print( )), i=1..1500);
%o A053245 (Haskell)
%o A053245 a053245 n = a053245_list !! (n-1)
%o A053245 a053245_list = f a053242_list where
%o A053245    f (x:x':xs) | x' == x+1 = x : f xs
%o A053245                | otherwise = f (x':xs)
%o A053245 -- _Reinhard Zumkeller_, Oct 16 2011
%Y A053245 Cf. A000203, A053226, A053238, A053239, A053240, A053241, A053242, A053243, A053244.
%K A053245 nonn
%O A053245 1,1
%A A053245 _Asher Auel_, Jan 10 2000