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A297645 Hexagonal numbers (A000384) in which parity of digits alternates. 4
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 (list; graph; refs; listen; history; text; internal format)
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 A189801

Adjacent sequences:  A297642 A297643 A297644 * A297646 A297647 A297648

KEYWORD

nonn,base

AUTHOR

Colin Barker, Jan 02 2018

STATUS

approved

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Last modified August 15 16:02 EDT 2020. Contains 336505 sequences. (Running on oeis4.)