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A264858 Integers n such that A007504(n) + 1 is a square. 1
0, 17, 539, 652, 6420 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Integers n such that the sum of the first n primes + 1 is a square.

Integers n such that A014284(n+1) is a square.

In A110996, it is commented that a(6) > 250000, if it exists.

a(6) > 50000000, if it exists. - Jon E. Schoenfield, Nov 29 2015

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

a(2) = 17 because A007504(17) + 1 = 440 + 1 = 441 is a square.

MATHEMATICA

t = Accumulate[Prime@ Range@ 100000]; Prepend[Select[Range@ 7000, IntegerQ@ Sqrt[t[[#]] + 1] &], 0] (* Michael De Vlieger, Nov 29 2015, after Zak Seidov at A007504 *)

Join[{0}, Position[Accumulate[Prime[Range[6500]]]+1, _?(IntegerQ[Sqrt[ #]]&)]] // Flatten (* Harvey P. Dale, Feb 12 2018 *)

PROG

(PARI) lista(nn) = { print1(0, ", "); s = 1; for(k=1, nn, s += prime(k); if(issquare(s), print1(k, ", ")); ); }

CROSSREFS

Cf. A007504, A014284, A033997, A110996.

Sequence in context: A114063 A214135 A193120 * A112716 A218351 A197395

Adjacent sequences:  A264855 A264856 A264857 * A264859 A264860 A264861

KEYWORD

nonn,more

AUTHOR

Altug Alkan, Nov 26 2015

STATUS

approved

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Last modified June 20 08:43 EDT 2021. Contains 345162 sequences. (Running on oeis4.)