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

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, 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, 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

Offset: 0

Author

Ctibor O. Zizka, Jan 21 2025

Keywords

• nonn
• base
• easy

Comments

The numbers n such that a(n) = k for any fixed k are a 10-automatic sequence. - Charles R Greathouse IV, Jan 21 2025

Examples

			a(10) = 0 as we do not accept zeros and ones in n.
a(22) = 0 as gcd(2,2) = 2.
a(25) = 25 as gcd(2,5) = 1.
a(1234567890) = a(23456789) = a(3579) = a(57) = 57.
Note that numbers n with even digits and numbers n containing digits 0 and 1 only disappear immediately and we get a(n) = 0.
		

Crossrefs

Cf. A004151, A004719, A059717.

Programs

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

Formula

a(n) <= 9875. There are 299 distinct values in this sequence. - Charles R Greathouse IV, Jan 21 2025