A245317 Concatenate n-th composite integer with n.
41, 62, 83, 94, 105, 126, 147, 158, 169, 1810, 2011, 2112, 2213, 2414, 2515, 2616, 2717, 2818, 3019, 3220, 3321, 3422, 3523, 3624, 3825, 3926, 4027, 4228, 4429, 4530, 4631, 4832, 4933, 5034, 5135, 5236, 5437, 5538, 5639, 5740
Offset: 1
Examples
a(8)=158 since 15 is the 8th composite integer.
Links
- Jens Kruse Andersen, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
w=Select[Range[2,57],!PrimeQ[#]&];Table[FromDigits[Flatten[{IntegerDigits[w[[n]]],IntegerDigits[n]}]],{n,1,40}] With[{cmps=Select[Range[100],CompositeQ]},#[[1]]10^IntegerLength[#[[2]]]+#[[2]]&/@Thread[{cmps,Range[Length[cmps]]}]] (* Harvey P. Dale, Jul 22 2025 *)