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URL: https://oeis.org/A309809

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A309809
a(n) is the concatenation of n and 2n+1.
3
13, 25, 37, 49, 511, 613, 715, 817, 919, 1021, 1123, 1225, 1327, 1429, 1531, 1633, 1735, 1837, 1939, 2041, 2143, 2245, 2347, 2449, 2551, 2653, 2755, 2857, 2959, 3061, 3163, 3265, 3367, 3469, 3571, 3673, 3775, 3877, 3979, 4081, 4183, 4285, 4387, 4489, 4591, 4693, 4795, 4897
OFFSET
1,1
LINKS
FORMULA
a(n) = n*10^(ceiling(log_10(2*n+1))) + 2*n + 1.
EXAMPLE
a(3)=37 is the concatenation of 3 and 7.
MAPLE
seq(n*10^(ceil(log[10](2*n+1)))+2*n+1, n=1..100);
MATHEMATICA
Table[FromDigits[Join[IntegerDigits[n], IntegerDigits[2n+1]]], {n, 50}] (* Harvey P. Dale, Jan 30 2024 *)
CROSSREFS
Sequence in context: A161603 A075033 A017533 * A264732 A298483 A344900
KEYWORD
nonn,base
AUTHOR
Robert Israel, Aug 17 2019
STATUS
approved