A132943 -id:A132943 - cp's OEIS frontend

A134733 Concatenation of next n imperfect numbers.

1, 23, 457, 891011, 1213141516, 171819202122, 23242526272930, 3132333435363738, 394041424344454647, 48495051525354555657, 5859606162636465666768, 697071727374757677787980

Offset: 1

Omar E. Pol, Nov 12 2007

Harvey P. Dale, Table of n, a(n) for n = 1..200

Cf. A053067, A132943, A133013. Imperfect numbers: A132999.

Module[{nn=120,in,len},in=Select[Range[nn],DivisorSigma[1,#]!=2#&];len= Floor[x/.Last[Solve[(x(x+1))/2==Length[in]]]];FromDigits[Flatten[ IntegerDigits/@ #]]&/@TakeList[in,Range[len]]] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Mar 01 2020 *)

A262576 Concatenation of the numbers from 1 to n but omitting 6.

Original entry on oeis.org

1, 12, 123, 1234, 12345, 123457, 1234578, 12345789, 1234578910, 123457891011, 12345789101112, 1234578910111213, 123457891011121314, 12345789101112131415, 1234578910111213141516, 123457891011121314151617, 12345789101112131415161718, 1234578910111213141516171819, 123457891011121314151617181920

Offset: 1

N. J. A. Sloane, Sep 25 2015

The only prime among the first 98 terms is a(6) = 123457. Does the sequence contain any other primes?
No additional primes through the first 2000 terms. - Harvey P. Dale, Sep 27 2018
Differs from A132943 at about the 28th terms.
No primes, other than a(6), through a(10000). - Robert Price, Nov 03 2018

Cf. A132943.
Cf. A007908, A262299, A262571-A262582.
See A262300 for more about this problem.

Module[{nn=20,c},c=Drop[Range[nn],{6}];Table[FromDigits[Flatten[ IntegerDigits/@ Take[c,n]]],{n,nn-1}]] (* Harvey P. Dale, Sep 27 2018 *)

cp's OEIS Frontend

A134733 Concatenation of next n imperfect numbers.

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