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A073684 Sum of next a(n) successive primes is prime. 10

%I #12 Aug 03 2014 14:01:18

%S 2,3,5,3,5,3,3,7,9,5,9,7,3,7,5,3,3,3,5,3,3,3,5,5,57,25,49,3,9,5,11,3,

%T 5,5,5,5,17,25,3,3,5,3,7,9,5,3,3,3,15,3,3,3,3,3,3,3,15,3,5,33,5,3,3,9,

%U 7,3,33,3,3,5,3,15,3,5,9,7,13,5,11,3,3,11

%N Sum of next a(n) successive primes is prime.

%C Group the primes such that the sum of each group is a prime. Each group from the second onwards should contain at least 3 primes: (2, 3), (5, 7, 11), (13, 17, 19, 23, 29), (31, 37, 41), (43, 47, 53, 59, 61), ... Sequence gives number of terms in each group.

%H T. D. Noe, <a href="/A073684/b073684.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1)=2 because sum of first two primes 2+3 is prime; a(2)=3 because sum of next three primes 5+7+11 is prime; a(3)=5 because sum of next five primes 13+17+19+23+29 is prime.

%t f[l_List] := Block[{n = Length[Flatten[l]], k = 3, r},While[r = Table[Prime[i], {i, n + 1, n + k}]; ! PrimeQ[Plus @@r], k += 2];Append[l, r]];Length /@ Nest[f, {{2, 3}}, 100] (* Ray Chandler, May 11 2007 *)

%t cnt = 0; Table[s = Prime[cnt+1] + Prime[cnt+2]; len = 2; While[! PrimeQ[s], len++; s = s + Prime[cnt+len]]; cnt = cnt + len; len, {n, 100}] (* _T. D. Noe_, Feb 06 2012 *)

%Y Cf. A073682(n) is the sum of terms in n-th group, A073683(n) is the first term in n-th group, A077279(n) is the last term in n-th group.

%K nonn

%O 1,1

%A _Amarnath Murthy_, Aug 11 2002

%E More terms from Gabriel Cunningham (gcasey(AT)mit.edu), Apr 10 2003

%E Extended by _Ray Chandler_, May 02 2007

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Last modified April 18 08:27 EDT 2024. Contains 371769 sequences. (Running on oeis4.)