A290148 a(n) is the integer resulting from the concatenation of the unit digit of n-1 to the digits of n without its own unit digit.
0, 1, 2, 3, 4, 5, 6, 7, 8, 91, 1, 11, 21, 31, 41, 51, 61, 71, 81, 92, 2, 12, 22, 32, 42, 52, 62, 72, 82, 93, 3, 13, 23, 33, 43, 53, 63, 73, 83, 94, 4, 14, 24, 34, 44, 54, 64, 74, 84, 95, 5, 15, 25, 35, 45, 55, 65, 75, 85, 96, 6, 16, 26, 36, 46, 56, 66, 76, 86, 97, 7
Offset: 1
Examples
For n=46, n-1 is 45, so a(46) is the concatenation of 5 (the unit digit of 45) and 4 (46 without 6), giving 54. For n=123, n-1 is 122, so a(123) is the concatenation of 2 (the unit digit of 122) and 12 (123 without 3), giving 212.
Links
- Michael S. Branicky, Table of n, a(n) for n = 1..20000
Programs
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Maple
f:= n -> (n-1 mod 10) * 10^ilog10(n) + floor(n/10);
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PARI
a(n) = my(precd = (n-1)%10); if (n < 10, precd, eval(concat(Str(precd), Str(n\10))));
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Python
def a(n): return 0 if n == 1 else int(str((n-1)%10)+ str(n)[:-1]) print([a(n) for n in range(1, 72)]) # Michael S. Branicky, Feb 22 2025
Formula
a(n) = (n-1 mod 10)*10^A004216(n) + floor(n/10). # Robert Israel, Jul 21 2017
Comments