A132932 -id:A132932 - cp's OEIS frontend

A283801 Concatenation of the first n odd composite numbers (A071904).

9, 915, 91521, 9152125, 915212527, 91521252733, 9152125273335, 915212527333539, 91521252733353945, 9152125273335394549, 915212527333539454951, 91521252733353945495155, 9152125273335394549515557, 915212527333539454951555763, 91521252733353945495155576365

Offset: 1

XU Pingya, Mar 17 2017

There are 3 primes in the first 5028 terms of this sequence, see A283802.

Eric Weisstein's World of Mathematics, Consecutive Number Sequences

Cf. A071904, A089933, A132932.

bb[1]=9;bb[n_]:=bb[n]=Which[PrimeQ[bb[n-1]+2]==False,bb[n-1]+2,PrimeQ[bb[n-1]+4]==False,bb[n-1]+4,True,bb[n-1]+6];coc[n_]:=FromDigits[Flatten[IntegerDigits[Table[bb[k],{k,1,n}]]]];Table[coc[n],14]
f[n_] := Block[{oc = cc = 0, k = 2}, While[oc <= n, If[ OddQ@ k && !PrimeQ@ k, cc = cc*10^IntegerLength[k] +k; oc++]; k++]; cc]; Array[f, 14] (* Robert G. Wilson v, Mar 17 2017 *)

A134795 Concatenation of first n positive oblong numbers.

Original entry on oeis.org

2, 26, 2612, 261220, 26122030, 2612203042, 261220304256, 26122030425672, 2612203042567290, 2612203042567290110, 2612203042567290110132, 2612203042567290110132156, 2612203042567290110132156182

Offset: 1

Omar E. Pol, Nov 26 2007

Oblong numbers are also called promic, pronic or heteromecic (numbers).

Cf. A007908, A132932. Oblong numbers: A002378.

Module[{nn=20,c},c=2*Accumulate[Range[nn]];Table[FromDigits[ Flatten[ IntegerDigits/@ Take[c,n]]],{n,nn}]] (* Harvey P. Dale, Sep 06 2015 *)

cp's OEIS Frontend

A283801 Concatenation of the first n odd composite numbers (A071904).

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