

A300021


For any k, the cumulative sum a(1) + a(2) + a(3) + ... + a(k) shows at least a digit 7.


2



7, 10, 20, 30, 3, 1, 2, 4, 40, 50, 5, 6, 9, 60, 23, 8, 19, 70, 11, 29, 63, 17, 80, 12, 18, 73, 27, 13, 14, 15, 16, 21, 22, 39, 33, 37, 64, 26, 74, 36, 65, 25, 75, 35, 66, 24, 76, 34, 67, 43, 53, 31, 28, 32, 38, 48, 90, 41, 49, 44, 46, 54, 56, 45, 55, 47, 83, 100, 110, 42, 51, 57, 58, 52, 120, 123, 77, 124, 86, 113, 87, 59, 61, 93, 97, 103, 101, 96, 104, 99, 102
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OFFSET

1,1


COMMENTS

The sequence starts with a(1) = 7 and is always extended with the smallest integer not yet present that does not lead to a contradiction.
A permutation of the natural numbers.


LINKS



EXAMPLE

7 shows a digit 7, of course (k = 1)
7 + 10 = 17 and 17 shows at least a digit 7 (k = 2)
7 + 10 + 20 = 37 and 37 shows at least a digit 7 (k = 3)
7 + 10 + 20 + 30 = 67 and 67 shows at least a digit 7 (k = 4)
7 + 10 + 20 + 30 + 3 = 70 and 70 shows at least a digit 7 (k = 5)
7 + 10 + 20 + 30 + 3 + 1 = 71 and 71 shows at least a digit 7 (k = 6)
...


CROSSREFS

Cf. A300015 (which is the lexicographic first sequence of positive integers without duplicate terms having this property).


KEYWORD

nonn,base


AUTHOR



STATUS

approved



