cp's OEIS Frontend

A379512 Erase digits 0 and 1 from decimal expansion of n. Then keep just the coprime digits; write 0 if all digits disappear.

%I A379512 #49 Jan 21 2025 10:54:50
%S A379512 0,0,2,3,4,5,6,7,8,9,0,0,2,3,4,5,6,7,8,9,2,2,0,23,0,25,0,27,0,29,3,3,
%T A379512 32,0,34,35,0,37,38,0,4,4,0,43,0,45,0,47,0,49,5,5,52,53,54,0,56,57,58,
%U A379512 59,6,6,0,0,0,65,0,67,0,0,7,7,72,73,74,75,76,0,78,79,8,8,0,83,0,85,0,87
%N A379512 Erase digits 0 and 1 from decimal expansion of n. Then keep just the coprime digits; write 0 if all digits disappear.
%C A379512 The numbers n such that a(n) = k for any fixed k are a 10-automatic sequence. - _Charles R Greathouse IV_, Jan 21 2025
%F A379512 a(n) <= 9875. There are 299 distinct values in this sequence. - _Charles R Greathouse IV_, Jan 21 2025
%e A379512 a(10) = 0 as we do not accept zeros and ones in n.
%e A379512 a(22) = 0 as gcd(2,2) = 2.
%e A379512 a(25) = 25 as gcd(2,5) = 1.
%e A379512 a(1234567890) = a(23456789) = a(3579) = a(57) = 57.
%e A379512 Note that numbers n with even digits and numbers n containing digits 0 and 1 only disappear immediately and we get a(n) = 0.
%o A379512 (PARI) a(n)=my(d=select(k->k>1, digits(n))); if(sum(i=1,#d, d[i]%2==0)>1, d=select(k->k%2,d)); if(sum(i=1,#d, d[i]%3==0)>1, d=select(k->k%3,d)); if(sum(i=1,#d, d[i]==5)>1, d=select(k->k!=5,d)); if(sum(i=1,#d, d[i]==7)>1, d=select(k->k!=7,d)); fromdigits(d) \\ _Charles R Greathouse IV_, Jan 21 2025
%Y A379512 Cf. A004151, A004719, A059717.
%K A379512 nonn,base,easy
%O A379512 0,3
%A A379512 _Ctibor O. Zizka_, Jan 21 2025