A127423 a(1) = 1; for n > 1, a(n) = n concatenated with n - 1.
1, 21, 32, 43, 54, 65, 76, 87, 98, 109, 1110, 1211, 1312, 1413, 1514, 1615, 1716, 1817, 1918, 2019, 2120, 2221, 2322, 2423, 2524, 2625, 2726, 2827, 2928, 3029, 3130, 3231, 3332, 3433, 3534, 3635, 3736, 3837, 3938, 4039, 4140, 4241, 4342, 4443, 4544, 4645
Offset: 1
Examples
a(12) = 1211 because 12 and 11 are two consecutive decreasing numbers.
Links
- Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Programs
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Haskell
a127423 n = a127423_list !! (n-1) a127423_list = 1 : map read (zipWith (++) (tail iss) iss) :: [Integer] where iss = map show [1..] -- Reinhard Zumkeller, Oct 07 2014 -
Magma
[Seqint(Intseq(n) cat Intseq(n+1)): n in [0..50]]; // Vincenzo Librandi, Nov 08 2016
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Maple
c2:=proc(x,y) local s: s:=proc(m) nops(convert(m,base,10)) end: x*10^s(y)+y: end: seq(c2(n,n-1),n=1..53); # Emeric Deutsch, Mar 07 2007
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Mathematica
Join[{1}, nxt[n_] := Module[{idn = IntegerDigits[n + 1], idn1 = IntegerDigits[n]}, FromDigits[Join[idn, idn1]]]; Array[nxt, 70]] (* Vincenzo Librandi, Nov 08 2016 *) nxt[{n_, a_}] := {n + 1, (n + 1) * 10^IntegerLength[n] + n}; NestList[nxt, {1, 1}, 50][[All, 2]] (* Harvey P. Dale, Jan 04 2019 *) -
PARI
a(n) = if (n==1, 1, eval(Str(n, n-1))); \\ Michel Marcus, Oct 14 2016
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Scala
val numerStrs = (1 to 50).map(Integer.toString(_)).toList val concats = (numerStrs.drop(1)) zip (numerStrs.dropRight(1)) concats.map(x => Integer.parseInt(x.1 + x._2)) // _Alonso del Arte, Oct 24 2019
Extensions
More terms from Emeric Deutsch, Mar 07 2007
Comments