A001369 -id:A001369 - cp's OEIS frontend

A066547 Let N = 123456789101112131415161718..., the concatenation of the natural numbers. a(n) is the n-digit number formed from the digits of N starting from the {n(n-1)/2 +1}th digit. Omit any leading zeros.

1, 23, 456, 7891, 1112, 131415, 1617181, 92021222, 324252627, 2829303132, 33343536373, 839404142434, 4454647484950, 51525354555657, 585960616263646, 5666768697071727, 37475767778798081, 828384858687888990, 9192939495969798991, 101102103104105106, 107108109110111112113

Offset: 1

Amarnath Murthy, Dec 16 2001

			1, 23, 456, 7891, 01112, 131415, 1617181, 92021222, 3... becomes 1, 23, 456, 7891, 1112, 131415, 1617181, 92021222, ...

Jason Bard, Table of n, a(n) for n = 1..1000 (first 71 terms from Vincenzo Librandi)

Cf. A100751, A007376, A033307, A066548.

Cf. A001369, A007923.

d = Flatten[IntegerDigits /@ Range[90]]; Table[FromDigits[Take[d, {n(n + 1)/2 + 1, (n + 1)(n + 2)/2}]], {n, 0, 17}] (* Robert G. Wilson v, Nov 22 2004 *)

N=[]; k=0; for(n=1,20, while(#NM. F. Hasler, May 08 2014

More terms from Larry Reeves (larryr(AT)acm.org), Dec 18 2001

A007923 Lengths increase by 1, digits cycle through positive digits.

Original entry on oeis.org

1, 23, 456, 7891, 23456, 789123, 4567891, 23456789, 123456789, 1234567891, 23456789123, 456789123456, 7891234567891, 23456789123456, 789123456789123, 4567891234567891, 23456789123456789, 123456789123456789

Offset: 1

R. Muller

C. Ashbacher, Some Problems Concerning the Smarandache Deconstructive Sequence, J. Recreational Mathematics, Vol. 29, No. 2, pages 82-84.
K. Atanassov, On the 4th Smarandache Problem, Notes on Number Theory and Discrete Mathematics, Sophia, Bulgaria, Vol. 5 (1999), No. 1, 33-35.

John Cerkan, Table of n, a(n) for n = 1..994
K. Atanassov, On Some of Smarandache's Problems
F. Smarandache, Only Problems, Not Solutions!
Eric Weisstein's World of Mathematics, Smarandache Sequences

Cf. A001369, A007924, A050234, A066547.

A007923[n_Integer] := Module[{result = 0},Do[ result += (Mod[(n*(n - 1)/2 + i - 1), 9] + 1) * 10^(n - i),{i, 1, n}   ]; result ]; Table[A007923[n],{n,18}] (* James C. McMahon, Dec 04 2023 *)

a(n)=my(m=(n*(n+1)/2-1)%9); sum(k=0,n-1,10^k*((m-k)%9+1))

a(n) = (10^9+1) a(n-9) - 10^9 a(n-18), n>=18. - corrected by Michael Somos, Sep 28 2002
a(n) = Sum_{i=1..n} ((n*(n-1)/2+i-1 mod 9)+1)*10^(n-i). - Vedran Glisic, Apr 08 2011
a(n) = floor(10^(n*(n+1)/2)*123456789/999999999) - 10^n*floor(10^(n*(n-1)/2)*123456789/999999999). - Néstor Jofré, Jun 03 2017

cp's OEIS Frontend

A066547 Let N = 123456789101112131415161718..., the concatenation of the natural numbers. a(n) is the n-digit number formed from the digits of N starting from the {n(n-1)/2 +1}th digit. Omit any leading zeros.

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