# [seqfan] Re: a(n) = a(n-1) + [sum of all digits present so far]

Farideh Firoozbakht f.firoozbakht at sci.ui.ac.ir
Thu Oct 1 21:59:48 CEST 2009

```

--- Farideh

Quoting Farideh Firoozbakht <f.firoozbakht at sci.ui.ac.ir>:

> Quoting Jonathan Post <jvospost3 at gmail.com>:
>
>> so the array begins (done by hand, needs checking)
>>
>> a(1) = k; a(n) = a(n-1) + sum of all decimal digits so far in the
>> sequence (row of array)
>>
>> ......|.n=1.|.n=2.|.n=3.|.n=4.|.n=5.|.n=6.|.n=7.|
>> k=1.|....1.|.....2.|.....5.|...13.|...25.|...44...|.71.|
>> k=2.|....2.|.....4.|.....8.|...16.|...39.|...90...|189.|
>> k=3.|....3.|.....6.|...21.|...45.|...99.|..216...|441.|
>>
>> and main diagonal 1, 4, 21, ...?
>
>  The correct values:
>
>    ......|.n=1.|.n=2.|.n=3.|.n=4.|.n=5.|.n=6.|.n=7.|
>   k=1.|....1.|.....2.|.....5.|...13.|...25.|...44...|.71.|
>   k=2.|....2.|.....4.|....10.|...17.|...32.|...52...|.79.|
>   k=3.|....3.|.....6.|....15.|...30.|...48.|...78...|123.|
>   k=4    4       8        20     34     55     86    131
>   k=5    5      10        16     29     53     85    130
>   k=6    6      12        21     33     51     75    111
>   ...
>
>  and main diagonal :
>
>  1, 4, 15, 34, 53, 75, 173, 209, 378, 419, 544, 597, 967, 1027, 1227,
>  1315, 1712, 2007, 2285, 2624, 2694, 2909, 4006, 4092, 4354, 4336,
>  4599, 5818, 5675, 6369, 6215, 7613, 8403, 8225, 9646, 9432, 10207,
>  11083, 11967, 12355, 12797, 14583, 15158, 16427, 16470, 17303, 18166,
>  19803, 20119, 19153, ...
>
>
>  --- Farideh
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> ----------------------------------------------------------------
> University of Isfahan (http://www.ui.ac.ir)

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University of Isfahan (http://www.ui.ac.ir)

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