%I #13 Oct 27 2023 22:00:45

%S 20,49,56,79,108,132,145,170,177,230,253,277,289,307,347,382,405,412,

%T 424,437,495,548,585,592,633,645,704,734,752,764,789,802,841,854,930,

%U 943,967,974,1005,1012,1053,1066,1130,1154,1179,1186,1216,1223,1264

%N Numbers n such that both A053238(n) and A053238(n+1) = 1.

%C Pairs of consecutive 1's occur uncommonly often in A053238.

%H Reinhard Zumkeller, <a href="/A053245/b053245.txt">Table of n, a(n) for n = 1..10000</a>

%p with(numtheory): f := [seq( `if`((sigma(i) > sigma(i+1)),i,print( )), i=1..5000)];

%p seq(`if`((f[i+2]-f[i+1]=1) and (f[i+1]-f[i]=1),i,print( )), i=1..1500);

%o (Haskell)

%o a053245 n = a053245_list !! (n-1)

%o a053245_list = f a053242_list where

%o f (x:x':xs) | x' == x+1 = x : f xs

%o | otherwise = f (x':xs)

%o -- _Reinhard Zumkeller_, Oct 16 2011

%Y Cf. A000203, A053226, A053238, A053239, A053240, A053241, A053242, A053243, A053244.

%K nonn

%O 1,1

%A _Asher Auel_, Jan 10 2000