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 A020641 a(n)-th prime is sum of first k primes for some k. 2
 1, 3, 7, 13, 45, 60, 977, 1108, 2470, 2687, 2784, 3126, 3470, 3977, 4100, 4511, 4644, 5668, 6148, 6627, 6963, 8407, 9767, 10379, 11007, 11220, 11449, 12111, 12332, 23080, 25001, 28009, 28357, 28709, 29060, 29404, 30824, 32271, 33397, 33764, 47735, 52278 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..2500 MATHEMATICA PrimePi /@ Select[ FoldList[Plus, 0, Prime@ Range@450], PrimeQ@# &] (* Robert G. Wilson v Sep 28 2006 *) PrimePi/@Select[Accumulate[Prime[Range[500]]], PrimeQ] (* Harvey P. Dale, Jun 05 2013 *) CROSSREFS Cf. A013916, A013917, A013918. Sequence in context: A289556 A086208 A090968 * A062736 A257716 A103564 Adjacent sequences:  A020638 A020639 A020640 * A020642 A020643 A020644 KEYWORD nonn AUTHOR N. J. A. Sloane, Renaud Lifchitz (100637.64(AT)CompuServe.COM), David W. Wilson STATUS approved

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Last modified December 10 16:44 EST 2018. Contains 318049 sequences. (Running on oeis4.)