A062887 - OEIS

%I #12 Apr 14 2023 22:14:03

%S 1,3,5,7,9,319,975,75,7531,19,197531975319,3197,75,5319,319,31,

%T 3197531975319,53197531975,1975319,975,531975,1975319753197,

%U 19753197531975,75319753197531,319753197531975319,753197531975319753

%N Smallest multiple of 2n+1 with the property that its digits are odd and each digit is two less (mod 10) than the previous digit, or 0 if no such number exists.

%C Conjecture: The only numbers n for which a(n)=0 are those for which 2*n+1 is divisible by 125. - _Sean A. Irvine_, Apr 14 2023

%e a(7) = 975 = 13*75 has decreasing odd digits.

%p l := 0:for i from 1 to 35 do for j from 1 to 5 do a := 0:for h from 1 to i do a := 10*a+((2*j+1-2*h) mod 10):end do:l := l+1:q[l] := a:end do:end do:s := seq(q[ll],ll=1..l); for i from 1 to 65 do k := 1:while((s[k] mod (2*i-1))>0) do k := k+1:end do: w[i] := s[k]:end do:seq(w[j],j=1..65);

%Y Cf. A062884, A062885.

%K nonn,base,easy

%O 0,2

%A _Amarnath Murthy_, Jun 28 2001

%E More terms from _Sascha Kurz_, Mar 25 2002