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A007826 Numbered stops on the Market-Frankford rapid transit (SEPTA) railway line in Philadelphia, PA USA. 6
2, 5, 8, 11, 13, 15, 30, 34, 40, 46, 52, 56, 60, 63, 69 (list; graph; refs; listen; history; text; internal format)



Formally abbreviated as The Blue Line (and known informally as 'The El'), the Market-Frankford Line extends East to West from slightly to the east of 2nd Street through the city line to the western suburbs at 63rd Street and then on to 69th Street Transportation Center, lined up almost entirely with the major dividing thoroughfare Market Street.  It is actually a subway at the eastern end of this portion and through to beyond the 40th Street stop (a(1)-a(9) represent subway stops), passing under the Schuylkill River (along with trolley lines 10, 11, 13, 34 and 36) closer to 30th than to 15th Street.  The only non-numbered stop on this end is suburban Milbourne between 63rd and 69th. The 'Frankford end' runs in a somewhat northeasterly direction and has all stops only with non-number names (and is entirely above ground).  The semi-express A and B versions of the train both skip certain stops at peak travel times, and the only regular trains are unmarked or one of these two versions. The train is substituted for with bus service during overnight hours. - James G. Merickel, Mar 19 2014


Ayshe Ozbekhan, Letter to N. J. A. Sloane, Oct 04, 1994.


Table of n, a(n) for n=1..15.

Brady Haran and N. J. A. Sloane, What Number Comes Next? (2018), Numberphile video

Wikipedia, Market-Frankford Line


a(n) = 2 + 3 n - binomial(n, 4) + 3 binomial(n, 5) + 7 binomial(n, 6) - 66 binomial(n, 7) + 248 binomial(n, 8) - 679 binomial(n, 9) + 1554 binomial(n, 10) - 3158 binomial(n, 11) + 5897 binomial(n, 12) - 10352 binomial(n, 13) + 17384 binomial(n, 14).


Cf. A000053, A000054, A001049.

Sequence in context: A167409 A082406 A215938 * A108589 A292988 A330144

Adjacent sequences:  A007823 A007824 A007825 * A007827 A007828 A007829




N. J. A. Sloane



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Last modified February 25 22:37 EST 2021. Contains 341618 sequences. (Running on oeis4.)