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A217555 Terms as well as digits are of alternating parity; this is the lexicographically earliest injective sequence with this property. 5

%I

%S 1,2,3,4,5,6,7,8,9,210,101,212,103,214,105,216,107,218,109,230,121,

%T 232,123,234,125,236,127,238,129,250,141,252,143,254,145,256,147,258,

%U 149,270,161,272,163,274,165,276,167,278,169,290,181,292,183

%N Terms as well as digits are of alternating parity; this is the lexicographically earliest injective sequence with this property.

%C The sum of two successive terms is odd and the sum of two successive digits is odd, too. The sequence could be started with an additional 0 and then be extended always with the smallest integer not yet present in the sequence and not leading to a contradiction. - _Eric Angelini_ and _Jean-Marc Falcoz_, Jan 31 2017

%H Carole Dubois, <a href="/A217555/b217555.txt">Table of n, a(n) for n = 1..5673</a>

%H Eric Angelini, <a href="http://list.seqfan.eu/pipermail/seqfan/2012-October/010252.html">Odd/even: integers and digits alternate</a>, SeqFan mailing list, Oct 06 2012

%F Conjectures from _Colin Barker_, Jan 16 2020: (Start)

%F G.f.: x*(1 + x + x^2 + x^3 + x^4 + x^5 + x^6 + x^7 + x^8 + 201*x^9 - 110*x^10 + 110*x^11 - 110*x^12 + 110*x^13 - 110*x^14 + 110*x^15 - 110*x^16 + 110*x^17 - 110*x^18 - 80*x^19) / ((1 - x)^2*(1 + x)*(1 - x + x^2 - x^3 + x^4)*(1 + x + x^2 + x^3 + x^4)).

%F a(n) = a(n-1) + a(n-10) - a(n-11) for n>20.

%F (End)

%o (PARI) {a(n,show=1,a=1,u)=for( i=2, n, u+=1<<a; show & print1(a","); for(t=1,9e9, bittest(u,t) & next; bittest(t+a,0) || next; !bittest(a%10 + t\10^(#Str(t)-1),0) & (t+=10^(#Str(t)-1)-1) & next; my(tt=t); while( tt>9, bittest( tt+0+tt\=10, 0 ) || next(2)); a=t; break )); a}

%Y Sequence A217556 is a simplified variant.

%Y See also A217559, A217560, where "parity" is replaced by "primality".

%K nonn,base,changed

%O 1,2

%A _Eric Angelini_ and _M. F. Hasler_, Oct 06 2012

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Last modified January 21 13:47 EST 2020. Contains 331113 sequences. (Running on oeis4.)