A328131 Erase all zero digits from decimal expansion of n. Then keep just the coprime digits; write 0 if all digits disappear.

1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 11, 12, 13, 14, 15, 16, 17, 18, 19, 2, 21, 0, 23, 0, 25, 0, 27, 0, 29, 3, 31, 32, 0, 34, 35, 0, 37, 38, 0, 4, 41, 0, 43, 0, 45, 0, 47, 0, 49, 5, 51, 52, 53, 54, 0, 56, 57, 58, 59, 6, 61, 0, 0, 0, 65, 0, 67, 0, 0, 7, 71, 72, 73, 74, 75, 76

Offset

1,2

Comments

Digit 0 in n is erased, non-coprime digits of n are erased. If all digits are erased, we write 0 for the result.

The digit 1 is never erased, e.g. repunits are fixed points of this procedure. - Chai Wah Wu, Apr 02 2020

Links

Daniel Suteu, Table of n, a(n) for n = 1..10000

Example

10 becomes 1 as we do not accept zeros in n, 22 becomes 0 as gcd(2,2) = 2, 25 becomes 25 as gcd(2,5) = 1, 1033 becomes 133 becomes 1, 1234567890 becomes 123456789 becomes 157. Note that numbers with even digits disappear immediately and we get 0.

Prog

(PARI) a(n) = my(D=digits(n)); D=select(d->d!=0, D); my(C=Set()); for(i=1, #D, for(j=i+1, #D, if(gcd(D[i], D[j]) != 1, C=concat(C, [D[i], D[j]])))); C=Set(C); fromdigits(select(d->!setsearch(C, d), D)); \\ Daniel Suteu, Oct 08 2019
(Python)
def A328131(n):
    s, tlist = str(n), ('2468', '369', '468', '5', '689', '7', '8', '9')
    dset = set('0'+''.join(t if t[0] in s and sum(s.count(d) for d in t) > 1 else '' for t in tlist))
    return int('0'+''.join(d for d in s if d not in dset)) # Chai Wah Wu, Apr 02 2020

Crossrefs

Cf. A320486.

Sequence in context: A059717 A004185 A068636 * A004719 A004151 A151765

Adjacent sequences: A328128 A328129 A328130 * A328132 A328133 A328134

Keyword

nonn,base

Author

Ctibor O. Zizka, Oct 04 2019

Status

approved