A336768 - OEIS

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A336768

Irregular triangle where the n-th row list the positive integers which can be written in two bases smaller than n as mutually-reversed strings of digit(s), for n>=4.

1, 1, 2, 22, 1, 2, 3, 7, 22, 1, 2, 3, 4, 7, 22, 87, 9831, 1, 2, 3, 4, 5, 7, 9, 17, 22, 51, 87, 102, 2601, 9831, 314767045, 1, 2, 3, 4, 5, 6, 7, 9, 17, 22, 51, 87, 91, 102, 220, 2601, 5258, 7491, 8283, 9831, 10516, 13541, 15774, 16566, 71500, 644765, 3552340, 314767045, 1427310725, 1848187230, 1916060910

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OFFSET

4,3

COMMENTS

Note that the last row with index 9 may still be incomplete.

If k is in row n then k is in row n+1. - David A. Corneth, Aug 04 2020

LINKS

Table of n, a(n) for n=4..66.

EXAMPLE

Triangle begins:

4| 1;

5| 1, 2, 22;

6| 1, 2, 3, 7, 22;

7| 1, 2, 3, 4, 7, 22, 87, 9831;

8| 1, 2, 3, 4, 5, 7, 9, 17, 22, 51, 87, 102, 2601, 9831, 314767045;

9| 1, 2, 3, 4, 5, 6, 7, 9, 17, 22, 51, 87, 91, 102, 220, 2601, 5258, 7491, ...

...

For n=4, there is a single integer whose base 2 and base 3 representations are each other reverse: it is 1 which is its own reverse.

CROSSREFS

Cf. A336733 (row index 10), A336827 (right diagonal).

Sequence in context: A278737 A162393 A328993 * A180700 A077526 A083764

Adjacent sequences: A336765 A336766 A336767 * A336769 A336770 A336771

KEYWORD

nonn,base,tabf

AUTHOR

Michel Marcus, Aug 04 2020

EXTENSIONS

a(32) from Graham Holmes, Aug 04 2020

More terms from Jinyuan Wang, Aug 04 2020

STATUS

approved