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A179996 Composite numbers n such that Sum_{k=0..q} d(k)*10^k is prime where d(k) are the q+1 distinct prime factors of n, d(0)< d(1) < ... < d(q). 0
15, 21, 33, 45, 51, 57, 63, 69, 75, 87, 91, 93, 99, 111, 129, 133, 135, 147, 153, 165, 171, 177, 183, 187, 189, 201, 207, 217, 219, 225, 253, 255, 261, 273, 279, 297, 303, 309, 327, 333, 363, 375, 387, 399, 405, 411, 427 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
435 is in the sequence because the prime divisors of 435 are {3, 5, 29} and
3 + 5*10 + 29*100 = 2953 is prime.
MAPLE
with(numtheory):T:=array(1..10) : for n from 1 to 1000 do:x:=factorset(n):
k:=nops(x):s:=0:for i from 1 to k do:s:=s+x[i]*10^(i-1) :od:if type(s, prime)=true
and k > 1 then printf(`%d, `, n):else fi:od:
MATHEMATICA
cnpQ[n_]:=Module[{pd=FactorInteger[n][[All, 1]]}, Length[pd]>1&&PrimeQ[ Total[ pd*10^Range[0, Length[pd]-1]]]]; Select[Range[500], cnpQ] (* Harvey P. Dale, Sep 02 2022 *)
CROSSREFS
Sequence in context: A177516 A127329 A043326 * A079814 A168354 A190358
KEYWORD
nonn,base
AUTHOR
Michel Lagneau, Jan 13 2011
STATUS
approved

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Last modified March 29 10:44 EDT 2024. Contains 371268 sequences. (Running on oeis4.)