A053233 - OEIS

%I #15 Oct 27 2023 22:00:45

%S 3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,24,25,26,27,28,

%T 29,30,33,34,35,36,37,40,41,42,43,44,45,46,47,48,49,50,51,52,53,55,56,

%U 57,58,60,61,62,63,64,65,66,69,70,71,72,73,76,77,78,79,80,81,82,83,85

%N Numbers n such that A053230(n) = 2.

%H Reinhard Zumkeller, <a href="/A053233/b053233.txt">Table of n, a(n) for n = 1..10000</a>

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

%p seq( `if`(f[i+1] - f[i] = 2,i,print( )), i=1..100);

%t Position[Differences@ Select[Range[170], Less @@ DivisorSigma[1, # + {0, 1}] &], 2][[All, 1]] (* _Michael De Vlieger_, Nov 19 2019 *)

%o (Haskell)

%o import Data.List (elemIndices)

%o a053233 n = a053233_list !! (n-1)

%o a053233_list = map (+ 1) $ elemIndices 2 a053230_list

%o -- _Reinhard Zumkeller_, May 07 2012

%Y Cf. A000203, A053224, A053230, A053231, A053232, A053234, A053235, A053236, A053237.

%K nonn

%O 1,1

%A _Asher Auel_, Jan 10 2000