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A231152
Least integer k such that prime(n+1) + ... + prime(n+k) > prime(1) + ... + prime(n).
2
2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 13, 13, 13, 14, 14, 14, 15, 15, 16, 16, 16, 17, 17, 17, 18, 18, 19, 19, 19, 20, 20, 20, 21, 21, 21, 22, 22, 23, 23, 23, 24, 24, 24, 25, 25, 25, 26, 26, 27
OFFSET
2,1
COMMENTS
a(n) is the greatest k such that 2*s(n) >= s(n+k), where s(n) is the n-th partial sum of primes.
FORMULA
a(n) = A231153(n) + 1.
EXAMPLE
5 <= 2 + 3 < 5 + 7, so a(2) = 2.
19 + 23 <= 2 + 3 + 5 + 7 + 11 + 13 + 17 < 19 + 23 + 27, so a(7) = 3.
MATHEMATICA
test = 0; u = Table[test = test + Prime[n]; tmp = 0; NestWhile[# + 1 &, n, test >= (tmp = tmp + Prime[#]) &] - n, {n, 1, 80}]; u + 1 (* Peter J. C. Moses, Nov 02 2013 *)
CROSSREFS
Sequence in context: A057810 A029917 A062300 * A086916 A008680 A120203
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Nov 09 2013
STATUS
approved