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 A171399 Prime(k), where k is such that (Sum_{i=1..k} prime(i)) / k is an integer. 94
 2, 83, 241, 6599, 126551, 1544479, 4864121, 60686737, 1966194317, 63481708607, 1161468891953, 14674403807731, 22128836547913, 399379081448429, 5410229663058299, 248264241666057167 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Corresponding values of k, Sum_{i=1..k} p_i, and (Sum_{i=1..k} p_i) / k are given in A045345, A050247 and A050248. No other solutions for p_k < 4011201392413. a(13) > 2*10^13. - Donovan Johnson, Aug 23 2010 a(16) > 5456843462009647. - Bruce Garner, Mar 06 2021 a(17) > 253814097223614463. - Paul W. Dyson, Sep 26 2022 LINKS Kaisa Matomäki, A note on the sum of the first n primes, Quart. J. Math. 61 (2010), pp. 109-115. FORMULA a(n) = A000040(A045345(n)). EXAMPLE 83 is the 23rd prime and (Sum_{i=1..23} p_i) / 23 = 874 / 23 = 38 (integer), so 83 is a term. MAPLE with(numtheory); P:=proc(i) local n, s; s:=0; for n from 1 to i do s:=s+ithprime(n); if s/n=trunc(s/n) then print(ithprime(n)); fi; od; end: # Paolo P. Lava, Feb 10 2012. MATHEMATICA t = {}; sm = 0; Do[sm = sm + Prime[n]; If[Mod[sm, n] == 0, AppendTo[t, Prime[n]]], {n, 100000}]; t (* T. D. Noe, Mar 19 2013 *) PROG (PARI) s=0; n=0; forprime(p=2, 1e7, s+=p; if(s%n++==0, print1(p", "))) \\ Charles R Greathouse IV, Jun 13 2012 CROSSREFS Cf. A085450 (smallest m > 1 such that m divides Sum_{k=1..m} prime(k)^n). Cf. A007504, A045345, A171399, A128165, A233523, A050247, A050248. Cf. A024450, A111441, A217599, A128166, A233862, A217600, A217601. Sequence in context: A007353 A108312 A175449 * A037069 A065591 A266201 Adjacent sequences: A171396 A171397 A171398 * A171400 A171401 A171402 KEYWORD nonn,more AUTHOR Jaroslav Krizek, Dec 07 2009 EXTENSIONS a(6) corrected and a(12) from Donovan Johnson, Aug 23 2010 a(13) from Robert Price, Mar 17 2013 a(14)-a(15) from Bruce Garner, Mar 06 2021 a(16) from Paul W. Dyson, Sep 26 2022 STATUS approved

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Last modified December 2 18:27 EST 2022. Contains 358510 sequences. (Running on oeis4.)