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A115742 Triangular numbers whose digit reversal is a semiprime (A001358). 2
6, 15, 28, 55, 78, 105, 120, 190, 496, 780, 903, 946, 1176, 1225, 1275, 1540, 1653, 1770, 1830, 1891, 2080, 3081, 3403, 3486, 3570, 3741, 3916, 4186, 4753, 5050, 5356, 5671, 6670, 7021, 7140, 7381, 7503, 7626, 8515, 8911, 9316, 9591, 9870 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

EXAMPLE

15=T(5) and 51=3*17 is semiprime.

MATHEMATICA

Select[Accumulate[Range[200]], PrimeOmega[FromDigits[Reverse[ IntegerDigits[ #]]]] == 2&] (* Harvey P. Dale, Nov 14 2013 *)

CROSSREFS

Cf. A001358, A115741.

Sequence in context: A164000 A212087 A134978 * A026102 A144519 A066995

Adjacent sequences:  A115739 A115740 A115741 * A115743 A115744 A115745

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, Jan 31 2006

STATUS

approved

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Last modified August 18 19:41 EDT 2017. Contains 290762 sequences.