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

Author

Colin Barker, Jan 02 2018

Keywords

• nonn
• base

Comments

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

Examples

			6903 is in the sequence because 6, 9, 0 and 3 have even and odd parity alternately.
		

Links

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

Crossrefs

Cf. A297644, A297646, A297647.

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

Programs

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

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))