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A225939 Numbers k that divide prime(k) + prime(k-1).

%I A225939 #26 Mar 18 2024 12:05:23
%S A225939 4,6,13,14,15,74,190,688,690,6456,40082,251735,251736,251738,399916,
%T A225939 637325,637326,637342,637343,2582372,2582434,4124456,4124458,6592686,
%U A225939 10553425,10553433,10553818,27067038,27067053,43435902,69709872,69709877,69709945,69709954,179992917
%N A225939 Numbers k that divide prime(k) + prime(k-1).
%H A225939 Giovanni Resta, <a href="/A225939/b225939.txt">Table of n, a(n) for n = 1..58</a> (terms < 1.5*10^12)
%e A225939 prime(3) + prime(4) = 5+7 = 12, because 12 is divisible by 4, the latter is in the sequence.
%e A225939 prime(5) + prime(6) = 11+13 = 24, because 24 is divisible by 6, the latter is in the sequence.
%t A225939 Select[Range[2,10^4],Divisible[Prime@#+Prime[#-1],#]&] (* _Giorgos Kalogeropoulos_, Aug 20 2021 *)
%o A225939 (C)
%o A225939 #include <stdio.h>
%o A225939 #define TOP (1ULL<<32)
%o A225939 int main() {
%o A225939   unsigned long long i, j, n = 1, prev;
%o A225939   char *c = (char*)malloc(TOP/2);
%o A225939   memset(c, 0, TOP/2);
%o A225939   for (prev = 2, i = 3; i < TOP; i += 2)
%o A225939     if (c[i>>1]==0) {
%o A225939       if ((i+prev) % ++n == 0)  printf("%llu, ", n);
%o A225939       for (prev = i, j = i*i>>1; j < TOP/2; j += i)  c[j] = 1;
%o A225939     }
%o A225939   return 0;
%o A225939 }
%o A225939 (Sage)
%o A225939 def is_a(n): return (nth_prime(n) + nth_prime(n-1)) % n == 0
%o A225939 filter(is_a, (2..1000))  # _Peter Luschny_, May 22 2013
%Y A225939 Cf. A001043, A023143, A045924, A066895, A066896.
%K A225939 nonn
%O A225939 1,1
%A A225939 _Alex Ratushnyak_, May 21 2013