# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a169834 Showing 1-1 of 1 %I A169834 #26 May 14 2023 18:17:00 %S A169834 34,86,94,142,202,214,218,231,243,244,302,375,394,446,604,634,664,698, %T A169834 903,922,1042,1106,1138,1262,1275,1310,1335,1346,1402,1642,1762,1833, %U A169834 1838,1886,1894,1925,1942,1982,2014,2055,2102,2134,2182,2218,2265,2306,2344,2362 %N A169834 Numbers k such that d(k-1) = d(k) = d(k+1). %H A169834 Alois P. Heinz, Table of n, a(n) for n = 1..10000 (first 1000 terms from Reinhard Zumkeller) %H A169834 Erich Friedman, What's Special About This Number? (See entry 34.) %F A169834 a(n) = A005238(n) + 1. - _Jon Maiga_ / _Georg Fischer_, Jun 24 2021 %p A169834 q:= n-> is(nops(map(numtheory[tau], {$n-1..n+1}))=1): %p A169834 select(q, [$1..3000])[]; # _Alois P. Heinz_, Jun 24 2021 %t A169834 d[n_] := DivisorSigma[0, n]; %t A169834 samedQ[n_] := d[n-1] == d[n] == d[n+1]; %t A169834 Select[Range[3000], samedQ] (* _Jean-François Alcover_, Aug 01 2018 *) %t A169834 1 + Flatten@Position[Differences@#&/@Partition[DivisorSigma[0, Range@3000], 3, 1], {0, 0}] (* _Hans Rudolf Widmer_, Feb 02 2023 *) %o A169834 (Haskell) %o A169834 a169834 n = a169834_list !! (n-1) %o A169834 a169834_list = f a051950_list [0..] where %o A169834 f (0:0:ws) (x:y:zs) = y : f (0:ws) (y:zs) %o A169834 f (_:v:ws) (_:y:zs) = f (v:ws) (y:zs) %o A169834 -- _Reinhard Zumkeller_, Aug 31 2014 %o A169834 (Python) %o A169834 from sympy import divisor_count as d %o A169834 def ok(n): return d(n-1) == d(n) == d(n+1) %o A169834 print(list(filter(ok, range(1, 2400)))) # _Michael S. Branicky_, Jun 24 2021 %Y A169834 Cf. A000005, A005238. %Y A169834 Cf. A051950. %K A169834 nonn %O A169834 1,1 %A A169834 _N. J. A. Sloane_, Jun 02 2010 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE