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A001704 a(n) = n concatenated with n + 1. 23
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) (1 to 50).map((n: Int) => n.toString + (n + 1).toString).mkString(", ") // Alonso del Arte, Nov 23 2018

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

N. J. A. Sloane

EXTENSIONS

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

STATUS

approved

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Last modified October 21 08:47 EDT 2019. Contains 328292 sequences. (Running on oeis4.)