A001704 a(n) = n concatenated with n + 1.

12, 23, 34, 45, 56, 67, 78, 89, 910, 1011, 1112, 1213, 1314, 1415, 1516, 1617, 1718, 1819, 1920, 2021, 2122, 2223, 2324, 2425, 2526, 2627, 2728, 2829, 2930, 3031, 3132, 3233, 3334, 3435, 3536, 3637, 3738, 3839, 3940, 4041, 4142, 4243, 4344, 4445, 4546

Offset

1,1

Comments

See A030457 for the indices of prime terms in this sequence. - Reinhard Zumkeller, Jun 27 2015 [Simplified by Jianing Song, Jan 27 2019]

Links

N. J. A. Sloane, Table of n, a(n) for n = 1..25000 (first 1000 terms from T. D. Noe)

Maple

f:=proc(i) i*10^(1+floor(evalf(log10(i+1), 10)))+i+1; end: # gives a(n) - N. J. A. Sloane, Aug 04 2012
# alternative Maple program:
a:= n-> parse(cat(n, n+1)):
seq(a(n), n=1..55);  # Alois P. Heinz, Jul 05 2018

Mathematica

Table[FromDigits@Flatten@IntegerDigits[{n, n + 1}], {n, 100}] (* T. D. Noe, Aug 09 2012 *)

Prog

(Haskell)
a001704 n = a001704_list !! (n-1)
a001704_list = map read (zipWith (++) iss $ tail iss) :: [Integer]
               where iss = map show [1..]
-- Reinhard Zumkeller, Oct 07 2014
(PARI) a(n)=eval(Str(n, n+1)) \\ Charles R Greathouse IV, Jul 23 2016
(Emacs Lisp)
;; Concatenation
(defun A001704 (n) (string-to-int (concat (int-to-string n) (int-to-string (1+ n)))))
;; Formula
(defun A001704 (n) (1+ n (* n (expt 10 (1+ (floor (log (1+ n) 10)))))))
(mapcar '(lambda (n) (cons n (A001704 n))) '(1 2 3 10 11 12 99 999)) => ((1 . 12) (2 . 23) (3 . 34) (10 . 1011) (11 . 1112) (12 . 1213) (99 . 99100) (999 . 9991000))
; Tim Chambers, Jul 07 2018
(Magma) [Seqint(Intseq(n+1) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Jul 08 2018
(Python) for n in range(1, 100): print(str(n)+str(n+1)) # David F. Marrs, Sep 17 2018
(Scala) val numerStrs = (1 to 50).map(Integer.toString(_)).toList
val concats = (numerStrs.dropRight(1)) zip (numerStrs.drop(1))
concats.map(x => Integer.parseInt(x._1 + x._2)) // Alonso del Arte, Oct 24 2019

Crossrefs

See A127421 for a version with offset 0.

Cf. A215027, A248378, A030457.

Sequence in context: A363820 A072485 A035333 * A127421 A112131 A233032

Adjacent sequences: A001701 A001702 A001703 * A001705 A001706 A001707

Keyword

nonn,base,easy

Author

N. J. A. Sloane

Extensions

More terms from Joshua Zucker and Jon E. Schoenfield, May 15 2007

Status

approved