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%I A297646 #10 Jul 14 2022 14:59:43
%S A297646 1,7,18,34,81,189,616,783,874,3010,4141,4347,5452,6943,8323,12145,
%T A297646 14707,18361,52345,69472,74563,78943,96727,129618,147258,163456,
%U A297646 214183,232105,250747,258727,270109,276723,278389,307476,309232,381616,389470,436183,450925
%N A297646 Heptagonal numbers (A000566) in which parity of digits alternates.
%C A297646 Intersection of A000566 and A030141. - _Felix Fröhlich_, Jan 03 2018
%H A297646 Harvey P. Dale, <a href="/load/view.php?a=aHR0cDovL29laXMub3JnL0EyOTc2NDYvYjI5NzY0Ni50eHQ">Table of n, a(n) for n = 1..500</a>
%e A297646 6943 is in the sequence because 6, 9, 4 and 3 have even and odd parity alternately.
%t A297646 Join[{1,7},Select[PolygonalNumber[7,Range[1000]],Union[Abs[Differences[ Boole[ OddQ[ IntegerDigits[ #]]]]]] =={1}&]] (* _Harvey P. Dale_, Jul 14 2022 *)
%o A297646 (PARI)
%o A297646 is_alt(n) = m=n; e=n%10; n\=10; while(n>0, f=n%10; if(e%2==f%2, return, e=f; n\=10)); return(m)
%o A297646 select(is_alt, vector(1000, n, (5*n^2-3*n)/2))
%Y A297646 Cf. A297644, A297645, A297647.
%Y A297646 Cf. A000566, A030141, A030152, A030160, A068882.
%K A297646 nonn,base
%O A297646 1,2
%A A297646 _Colin Barker_, Jan 02 2018

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