|
| |
|
|
A297646
|
|
Heptagonal numbers (A000566) in which parity of digits alternates.
|
|
3
|
|
|
|
1, 7, 18, 34, 81, 189, 616, 783, 874, 3010, 4141, 4347, 5452, 6943, 8323, 12145, 14707, 18361, 52345, 69472, 74563, 78943, 96727, 129618, 147258, 163456, 214183, 232105, 250747, 258727, 270109, 276723, 278389, 307476, 309232, 381616, 389470, 436183, 450925
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
COMMENTS
|
Intersection of A000566 and A030141. - Felix Fröhlich, Jan 03 2018
|
|
|
LINKS
|
Table of n, a(n) for n=1..39.
|
|
|
EXAMPLE
|
6943 is in the sequence because 6, 9, 4 and 3 have even and odd parity alternately.
|
|
|
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, (5*n^2-3*n)/2))
|
|
|
CROSSREFS
|
Cf. A297644, A297645, A297647.
Cf. A000566, A030141, A030152, A030160, A068882.
Sequence in context: A000566 A225248 A301709 * A320281 A169677 A263876
Adjacent sequences: A297643 A297644 A297645 * A297647 A297648 A297649
|
|
|
KEYWORD
|
nonn,base
|
|
|
AUTHOR
|
Colin Barker, Jan 02 2018
|
|
|
STATUS
|
approved
|
| |
|
|
