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 A001704 a(n) = n concatenated with n + 1. 26
 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 (list; graph; refs; listen; history; text; internal format)
 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) FORMULA a(n) = n*10^(1 + floor(log(n+1))) + n + 1, with n >= 1. - Paolo P. Lava, May 09 2008 MAPLE P:=proc(n) local a, i; for i from 1 by 1 to n do a:=i*10^(1+floor(evalf(log10(i+1), 10)))+i+1; print(a); od; end: P(100); # Paolo P. Lava, May 09 2008 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: A228157 A072485 A035333 * A127421 A112131 A233032 Adjacent sequences:  A001701 A001702 A001703 * A001705 A001706 A001707 KEYWORD nonn,base,easy AUTHOR EXTENSIONS More terms from Joshua Zucker and Jon E. Schoenfield, May 15 2007 STATUS approved

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Last modified October 28 06:26 EDT 2020. Contains 338048 sequences. (Running on oeis4.)