A297646 - OEIS

A297646

Heptagonal numbers (A000566) in which parity of digits alternates.

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

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OFFSET

1,2

COMMENTS

Intersection of A000566 and A030141. - Felix Fröhlich, Jan 03 2018

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..500

EXAMPLE

6943 is in the sequence because 6, 9, 4 and 3 have even and odd parity alternately.

MATHEMATICA

Join[{1, 7}, Select[PolygonalNumber[7, Range[1000]], Union[Abs[Differences[ Boole[ OddQ[ IntegerDigits[ #]]]]]] =={1}&]] (* Harvey P. Dale, Jul 14 2022 *)

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