|
%I #9 Aug 17 2016 05:24:22
%S 21,36,8277,22987,31199,59577,2092101,25224589,29963201,564423629,
%T 1353149983,30011570617,37090609821,392629311959
%N Decimal encoding of the prime factorization of n is a multiple of n.
%C If n = p_1^e_1 * ... * p_r^e_r with p_1 < ... < p_r, then the decimal encoding is p_1 e_1...p_r e_r. For example, 15 = 3^1 * 5^1, so has decimal encoding 3151.
%C a(12) > 10^10. [From _Donovan Johnson_, Mar 26 2010]
%C a(15) > 10^12. - _Giovanni Resta_, Aug 17 2016
%e The prime factorization of 21 = 3^1 * 7^1 with corresponding encoding 3171. 3171 = 21 * 151, a multiple of 21. So 21 is a term of the sequence.
%t Select[Range[100000], Mod[FromDigits[Flatten[IntegerDigits /@ Flatten[FactorInteger[ # ]]]], # ] ==0 &]
%o (PARI) {a067598(a,b) = local(n,v); for(n=max(2,a),b,v=factor(n); if(eval(concat(vector(matsize(v)[1],k,concat(vector(matsize(v)[2],j,Str(v[k,j]))))))%n==0,print1(n,",")))}
%K base,easy,nonn
%O 1,1
%A _Joseph L. Pe_, Jan 31 2002
%E Edited and extended by _Robert G. Wilson v_, Feb 02 2002
%E Two more terms from _Klaus Brockhaus_, Feb 20 2002
%E a(10)-a(11) from _Donovan Johnson_, Mar 26 2010
%E a(12)-a(14) from _Giovanni Resta_, Aug 17 2016
|
