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A127421
Numbers whose decimal expansion is a concatenation of 2 consecutive increasing nonnegative numbers.
10
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
1,2
COMMENTS
Primes in the sequence are in A030458. - Bruno Berselli, Mar 25 2015
a(n) always has an even number of digits unless n is in A103456. - Alonso del Arte, Oct 30 2019
LINKS
EXAMPLE
a(1) = "0,1" = 1.
a(13) = "12,13" = 1213.
MAPLE
a:= n-> parse(cat(n-1, n)):
seq(a(n), n=1..55); # Alois P. Heinz, Jul 05 2018
MATHEMATICA
nMax = 49; digitsList = IntegerDigits[Range[0, nMax]]; Table[FromDigits[Flatten[{digitsList[[n]], digitsList[[n + 1]]}]], {n, nMax - 1}] (* Alonso del Arte, Oct 24 2019 *)
Table[FromDigits[Flatten[IntegerDigits/@{n, n+1}]], {n, 0, 50}] (* Harvey P. Dale, May 16 2020 *)
PROG
(Magma) [Seqint(Intseq(n+1) cat Intseq(n)): n in [0..50]]; // Bruno Berselli, Mar 25 2015
(Python) for n in range(100): print(int(str(n)+str(n+1))) # David F. Marrs, Sep 17 2018
(Scala) val numerStrs = (0 to 49).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
A variant of A001704.
For concatenations of exactly k consecutive integers see A000027 (k = 1), A127421 (k = 2), A001703 (k = 3), A279204 (k = 4). For 2 or more see A035333.
Sequence in context: A072485 A035333 A001704 * A112131 A233032 A088997
KEYWORD
nonn,base,easy
AUTHOR
Artur Jasinski, Jan 14 2007
EXTENSIONS
More terms from Joshua Zucker, May 15 2007
STATUS
approved