

A302940


Lexicographically first sequence of distinct terms such that the product of any two terms is not a term of the sequence, and the product of any two digits is not a digit of the sequence.


2



2, 3, 4, 5, 7, 9, 44, 47, 49, 54, 55, 57, 59, 74, 75, 77, 79, 95, 97, 99, 444, 445, 447, 449, 454, 455, 457, 459, 474, 477, 479, 494, 497, 499, 544, 545, 547, 549, 554, 555, 557, 559, 574, 575, 577, 579, 594, 595, 597, 599, 744, 745, 747, 749, 754, 755, 757, 759, 774, 775, 777, 779, 794, 795, 797, 799
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OFFSET

1,1


COMMENTS

a(1) = 0 is forbidden as [0 x a(n)] = 0, a term of the sequence;
a(1) = 1 is forbidden as [1 x a(n)] = a(n), a term of the sequence;
a(1) = 2 is ok;
a(2) = 3 is ok;
a(3) = 4 is ok, but no more digits 2 as (2 x 2) = 4;
a(4) = 5 is ok as (5 x 2), (5 x 3), (5 x 4)... are > 9;
a(5) = 6 is forbidden as (2 x 3) = 6;
a(5) = 7 is ok as (7 x 2), (7 x 3), (7 x 4)... are > 9;
a(6) = 8 is forbidden as (2 x 4) = 8;
a(6) = 9 is ok, but no more digits 3 as (3 x 3) = 9.
The other terms of the sequence use only digits 4,5,7 and 9.


LINKS

JeanMarc Falcoz, Table of n, a(n) for n = 1..1002


EXAMPLE

2 x 3 = 6 and there is no term or digit 6 in the sequence;
2 x 4 = 8 and there is no term or digit 8 in the sequence;
2 x 5 = 10 and there is no term 10 in the sequence;
2 x 6 = 12 and there is no term 12 in the sequence;
2 x 7 = 14 and there is no term 14 in the sequence;
2 x 9 = 18 and there is no term 18 in the sequence;
3 x 4 = 12 and there is no term 12 in the sequence;
3 x 5 = 15 and there is no term 15 in the sequence;
etc.


CROSSREFS

Cf. A302938 where the word “product” is replaced by “sum”.
Sequence in context: A293535 A261170 A051453 * A272072 A118463 A214652
Adjacent sequences: A302937 A302938 A302939 * A302941 A302942 A302943


KEYWORD

nonn,base


AUTHOR

JeanMarc Falcoz and Eric Angelini, Apr 16 2018


STATUS

approved



