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A298978 Lexicographic first sequence of positive integers such that a(n)*a(n+1) has a digit 8, and no term occurs twice. 9
1, 8, 6, 3, 16, 5, 17, 4, 2, 9, 12, 7, 14, 13, 22, 19, 15, 32, 24, 20, 29, 27, 18, 10, 28, 11, 26, 23, 21, 38, 31, 35, 25, 33, 36, 30, 46, 40, 37, 34, 42, 39, 47, 44, 41, 45, 53, 54, 52, 49, 58, 48, 51, 55, 56, 43, 60, 63, 61, 62, 59, 65, 69, 70, 64, 57, 50, 76, 68, 66, 71, 73, 67, 72, 74, 77, 79, 82, 83, 86, 78, 75, 91, 80, 81, 84, 87, 90, 89 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

A permutation of the positive integers.

LINKS

Table of n, a(n) for n=1..89.

EXAMPLE

a(1) = 1 is the least positive integer, and a(1) has no other constraint to satisfy.

a(2) = 8 is the least positive integer > a(1) = 1 such that a(2)*a(1) = 8 has a digit 3.

a(3) = 6 is the least positive integer not in {1, 8} such that a(3)*a(2) (= 48) has a digit 8: All smaller choices 2, 4, ..., 7 do not satisfy this.

a(4) = 3 is the least positive integer not in {1, 6, 8} such that a(4)*a(3) (= 18) has a digit 8: The only smaller choice 2 does not satisfy this.

PROG

(PARI) A298978(n, f=1, d=8, a=1, u=[a])={for(n=2, n, f&&if(f==1, print1(a", "), write(f, n-1, " "a)); for(k=u[1]+1, oo, setsearch(u, k)&&next; setsearch(Set(digits(a*k)), d)&&(a=k)&&break); u=setunion(u, [a]); while(#u>1&&u[2]==u[1]+1, u=u[^1])); a}

CROSSREFS

Cf. A299402, A298974, ..., A298979: analog with digit 2, 4, ..., 9.

Cf. A299957, A299969, ..., A299988 (analog with addition instead of multiplication, and different digits).

Sequence in context: A084895 A154719 A263181 * A199151 A177154 A059631

Adjacent sequences:  A298975 A298976 A298977 * A298979 A298980 A298981

KEYWORD

nonn,base

AUTHOR

M. F. Hasler, Feb 22 2018

STATUS

approved

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Last modified December 6 08:53 EST 2019. Contains 329788 sequences. (Running on oeis4.)