A297645 Hexagonal numbers (A000384) in which parity of digits alternates.

1, 6, 45, 276, 325, 496, 561, 630, 703, 2145, 2701, 6903, 8385, 10585, 14365, 18721, 25878, 38503, 47278, 74305, 89676, 90525, 107416, 109278, 147696, 149878, 210925, 254541, 303810, 345696, 349030, 383250, 454581, 527878, 561270, 674541, 705078, 709836

Offset

1,2

Comments

Intersection of A000384 and A030141. - Felix Fröhlich, Jan 03 2018

Links

Robert Israel, Table of n, a(n) for n = 1..1000

Example

6903 is in the sequence because 6, 9, 0 and 3 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*(2*n-1), n=1..10^4)]); # Robert Israel, Jan 05 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, (4*n^2-2*n)/2))

Crossrefs

Cf. A297644, A297646, A297647.

Cf. A000384, A030141, A030152, A030160, A068882.

Sequence in context: A258623 A003486 A262415 * A201191 A214982 A360021

Adjacent sequences: A297642 A297643 A297644 * A297646 A297647 A297648

Keyword

nonn,base

Author

Colin Barker, Jan 02 2018

Status

approved