login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A270424 Numbers m such that m^2 is the sum of multiple sequential prime squares. 1
586, 6088, 8174, 11585, 11707, 270106, 288818, 375661, 724909, 732910, 937423, 1141509, 1326970, 1619934, 1776809, 1930140, 2239367, 2489647, 3063687, 3649371, 3790381, 3941615, 4193988, 4821615, 4887146, 5572173, 6047246, 6192322, 8088524, 9158347 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

m^2 = Sum_{i=k..j} prime(i)^2 is a square, for some k,j, j>k.

The 30 numbers given above are the only m values for all possible summations where the resulting m^2 <10^14 (m <10^7). This requires searching from k values up to ~482,000, but with decreasing j-k ranges for efficiency.

Values of k that yield results begin: 13, 37, 101, 183, 235, 588, 805, 891, 1066... but do not correspond fully to the order of the m values shown.

Number of sequential summands (i.e., j-k+1) vary widely, with the smallest being 28 and largest being 10360, for those m values listed above.

Also note j-k+1 mod 8 = {0,1,4}, as expected, since prime(i)^2 mod 24 = 1, for i>2.

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..164 (terms < 4*10^9)

Giovanni Resta, Details of the sums, for a(n) < 4*10^9

EXAMPLE

586 is in the sequence because 586^2 = 343396 = Sum_{i=13..40} prime(i)^2.

MATHEMATICA

lim = 20000^2; L={}; P=Prime[Range[2 + PrimePi@ Sqrt[lim/2]]]^2; i = 1; While[ P[[i]] + P[[i+1]] <= lim, s = P[[i]]; j = i+1; While[(s += P[[j++]]) <= lim, If[IntegerQ@ Sqrt@ s, AppendTo[L, Sqrt@ s]]]; i++]; Union@L (* Giovanni Resta, Apr 13 2016 *)

result = {}; k = 3; While[k <= 481167, resultk = {}; sump = 0;

count = 0; i = k; While[sump < 10^14, sump += Prime[i]^2;

  If[Mod[i - k + 1, 8] == 1 || Mod[i - k + 1, 8] == 0 ||

    Mod[i - k + 1, 8] == 4, If[i != k && IntegerQ[Sqrt[sump]], count++;

    AppendTo[resultk, {k, i - k + 1, sump}]]]; i++];

If[count > 0, AppendTo[result, resultk]]; k++]; result (* Only for k>2, so as to use index values to reduce repeated checking Sqrt - Richard R. Forberg, Apr 14 2016  *)

CROSSREFS

Cf. A001248, A061890.

Sequence in context: A051988 A261263 A251476 * A196888 A142836 A093229

Adjacent sequences:  A270421 A270422 A270423 * A270425 A270426 A270427

KEYWORD

nonn

AUTHOR

Richard R. Forberg, Mar 30 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified January 17 07:18 EST 2018. Contains 297787 sequences.