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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

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Last modified May 16 11:35 EDT 2022. Contains 353704 sequences. (Running on oeis4.)