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A111073 Numbers n such that the sum of the smallest and largest prime factors of n divides n. 1
4, 8, 16, 32, 64, 126, 128, 252, 256, 378, 390, 504, 512, 630, 756, 780, 798, 882, 1008, 1024, 1134, 1150, 1170, 1260, 1512, 1560, 1596, 1764, 1890, 1950, 2016, 2046, 2048, 2268, 2300, 2340, 2394, 2520, 2646, 2730, 2886, 3024, 3120, 3150, 3192, 3402, 3450 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All terms are even. - Harvey P. Dale, Sep 03 2015

Powers of 2 and numbers of the form 2 * p * (p + 2) * k where p is prime, p+2 isn't and k > 0 is p-smooth. - David A. Corneth, Sep 28 2019

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from Harvey P. Dale)

EXAMPLE

126 = 2*3^2*7, with smallest and largest prime factors 2 and 7, sum = 9, and 126 is divisible by 9; so 126 is in the sequence.

MATHEMATICA

slpdQ[n_]:=Module[{f=Transpose[FactorInteger[n]][[1]]}, Divisible[n, Total[ {First[f], Last[f]}]]]; Select[Range[4000], slpdQ] (* Harvey P. Dale, Sep 03 2015 *)

PROG

(PARI) lista(n) = {for (i=2, n, my(fac = factor(i), s = fac[1, 1] + fac[matsize(fac)[1], 1]); if (i % s == 0, print1(i, ", ")); ); } \\ Michel Marcus, May 18 2013

CROSSREFS

Sequence in context: A145108 A108569 A196875 * A298807 A005934 A085629

Adjacent sequences:  A111070 A111071 A111072 * A111074 A111075 A111076

KEYWORD

easy,nonn

AUTHOR

Joseph L. Pe, Oct 10 2005

STATUS

approved

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Last modified March 29 17:23 EDT 2020. Contains 333116 sequences. (Running on oeis4.)