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

Author

XU Pingya, Mar 17 2017

Keywords

• base
• nonn
• easy

Comments

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

Links

• Eric Weisstein's World of Mathematics, Consecutive Number Sequences

Crossrefs

Cf. A071904, A089933, A132932.

Programs

Mathematica

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 *)