A297647 Octagonal numbers (A000567) in which parity of digits alternates.

1, 8, 21, 65, 96, 341, 3816, 4961, 8321, 8965, 9296, 10325, 12545, 14145, 14981, 16725, 18565, 23056, 27456, 36741, 63656, 65416, 103416, 105656, 169456, 181056, 210145, 216545, 232965, 236321, 256961, 412181, 430165, 434721, 569416, 614721, 658945, 698901

Offset

1,2

Comments

Intersection of A000567 and A030141. - Felix Fröhlich, Jan 03 2018

Links

Robert Israel, Table of n, a(n) for n = 1..2000

Example

8321 is in the sequence because 8, 3, 2 and 1 have even and odd parity alternately.

Maple

filter:= proc(n) local L;
  if n < 10 then return true fi;
  L:= convert(n, base, 10) mod 2;
  not has(L[2..-1]-L[1..-2], 0)
end proc:
select(filter, [seq(n*(3*n-2), n=1..1000)]); # Robert Israel, Jan 03 2018

Prog

(PARI)
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)
select(is_alt, vector(1000, n, (6*n^2-4*n)/2))

Crossrefs

Cf. A297644, A297645, A297646.

Cf. A000567, A030141, A030152, A030160, A068882.

Sequence in context: A080144 A241522 A096018 * A267144 A240516 A079386

Adjacent sequences: A297644 A297645 A297646 * A297648 A297649 A297650

Keyword

nonn,base

Author

Colin Barker, Jan 02 2018

Status

approved