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A085273 Difference between n-th composite number and its largest prime divisor. 3

%I #10 Jun 20 2019 17:40:08

%S 2,3,6,6,5,9,7,10,14,15,15,14,11,21,20,13,24,21,25,30,22,17,28,33,19,

%T 26,35,35,33,40,23,45,42,45,34,39,51,44,49,38,29,55,31,56,62,52,55,51,

%U 46,63,69,37,70,57,66,65,75,78,41,77,68,43,58,77,85,78,69,62,47,76,93,91

%N Difference between n-th composite number and its largest prime divisor.

%H Ivan Neretin, <a href="/A085273/b085273.txt">Table of n, a(n) for n = 1..10000</a>

%e For 91=7*13 we have 91-13 = 78.

%e For 92=2*2*23 we have 92-23 = 69.

%t DeleteCases[Table[n - FactorInteger[n][[-1, 1]], {n, 100}], 0 _] (* _Ivan Neretin_, Jun 20 2019 *)

%o (PARI) cminusp2(n) = { for(x=2,n, forstep(p=x,2,-1, if(isprime(p) & x%p==0 & isprime(x)==0,print1(x-p,","); break); ) ) }

%Y Cf. A002808, A085271.

%K easy,nonn

%O 1,1

%A _Cino Hilliard_, Aug 12 2003

%E Offset corrected by _Ivan Neretin_, Jun 20 2019

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Last modified April 20 12:36 EDT 2024. Contains 371844 sequences. (Running on oeis4.)