login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

a(0) = 2; a(n) = smallest multiple of a(n-1), not a multiple of 10, that contains all the digits of a(n-1).
6

%I #21 Jan 17 2020 10:41:30

%S 2,12,132,10032,7213008,1017034128,1374013106928,1826063419107312,

%T 10056131249023967184,26980600141131303954672,

%U 287019624301354811469800736,130880948681417794030229135616

%N a(0) = 2; a(n) = smallest multiple of a(n-1), not a multiple of 10, that contains all the digits of a(n-1).

%C "Contains all the digits of a(n-1)" means it can be obtained by inserting digits anywhere in a permutation of digits of a(n-1) (prefix, suffix or insertion), but zeros are not to be suffixed as to avoid the trivial solution a(n-1)*10.

%C The 5th term suggested by the original author was 1103520 = 110 * 10032. This lets us guess that the intended definition was to exclude the trivial solution a(n-1)*10, but not any multiple of 10. But the definition has been amended to exclude multiples of 10 completely, and a(5) has been changed to the current value. Similarly, after a(8) = 1826063419107312, there would be a nontrivial solution a(9) = a(8)*5 = 2401273396126115280, where the final 0 is not appended but one of the 0's already in a(8). This is however excluded by the definition. - _M. F. Hasler_, Nov 18 2018

%o (PARI) A077696(n,a=2)={my(c(n,c=vector(10))=for(i=1,#n=digits(n),c[n[i]+1]++);c); for(i=1,n,my(cc=c(a));for(k=2,oo, k%5 && vecmin(c(k*a)-cc)>=0 && (a*=k) && break));a} \\ n=1 and optional 2nd arg as starting value yields next term:

%o print1(a=2);for(n=0,10,print1(","a=A077696(1,a))) \\ _M. F. Hasler_, Nov 18 2018

%Y Cf. A077697.

%K base,nonn

%O 0,1

%A _Amarnath Murthy_, Nov 18 2002

%E Corrected and extended by _Ray Chandler_, Jul 25 2003

%E Definition edited by _M. F. Hasler_, Nov 18 2018