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A336669 a(n) is the number of n-digit terms in A336668 (assuming 0 has 0 digit). 2

%I

%S 1,9,25,54,93,24,192,72,464,606,40,9,302,9,88,69,464,9,1056,9,108,117,

%T 25,9,775,24,25,606,156,9,207,9,464,54,25,87,1166,9,25,54,479,9,255,9,

%U 93,621,25,9,775,72,40,54,93,9,1056,24,527,54,25,9,317,9,25

%N a(n) is the number of n-digit terms in A336668 (assuming 0 has 0 digit).

%C This sequence is bounded as the decimal representation of any term in A336668 is fully determined by at most 9 of its leading digits.

%H Rémy Sigrist, <a href="/A336669/b336669.txt">Table of n, a(n) for n = 0..10000</a>

%H Rémy Sigrist, <a href="/A336669/a336669.gp.txt">PARI program for A336669</a>

%F a(n) = 9 iff n is 11-rough (A008364).

%F a(k*n) >= a(n) for any n >= 0 and k > 0.

%F Apparently, when n > 0, a(n) = a(gcd(n, 2^3 * 3^2 * 5 * 7)).

%e For n = 2:

%e - let m be a two-digit term of A336668 (10 <= m <= 99),

%e - if m starts with an odd digit, say d = 1, 3, 5, 7 or 9, then m ends with d,

%e - if m starts with an even digit, say d = 2, 4, 6 or 8, then m ends with any even digit, say t = 0, 2, 4, 6 or 8,

%e - so a(2) = 5 + 4*5 = 25.

%o (PARI) See Links section.

%Y Cf. A008364, A336668.

%K nonn,base

%O 0,2

%A _Rémy Sigrist_, Jul 29 2020

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Last modified February 4 13:32 EST 2023. Contains 360055 sequences. (Running on oeis4.)