A076305 - OEIS

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A076305

Numbers k such that prime(k) + prime(k+1) + prime(k+2) is a square.

6, 12, 59, 65, 112, 965, 1029, 1455, 1706, 1830, 1890, 2573, 3457, 4490, 4664, 5609, 7927, 9130, 10078, 10143, 12597, 18248, 19727, 20086, 20887, 21708, 22739, 25041, 26536, 28511, 29346, 29664, 29774, 33387, 39945, 40677, 46136, 49869, 58135

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

See A076304 for the square roots of the sums of the three primes.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..600 from Harvey P. Dale)

FORMULA

a(n) = A000720(A206279(n)). - M. F. Hasler, Jan 03 2020

EXAMPLE

6 is a term because prime(6) + prime(7) + prime(8) = 13 + 17 + 19 = 49 = 7^2.

MATHEMATICA

Select[Range[60000], IntegerQ[Sqrt[Sum[Prime[k], {k, #, # + 2}]]] &] (* Ray Chandler, Sep 26 2006 *)

Position[Partition[Prime[Range[60000]], 3, 1], _?(IntegerQ[Sqrt[ Total[ #]]]&), 1, Heads->False]//Flatten (* Harvey P. Dale, Sep 28 2018 *)

PROG

(PARI) n=0; p=2; q=3; forprime(r=5, 1e9, n++; if(issquare(p+q+r), print1(n", ")); p=q; q=r) \\ Charles R Greathouse IV, Apr 07 2017

(Magma) [k:k in [1..60000]| IsSquare(&+[NthPrime(k+m):m in [0, 1, 2]])]; // Marius A. Burtea, Jan 04 2020

CROSSREFS

Cf. A076304 (square roots of sums), A080665 (squares = sums), A206279 (lesser of the primes).

Cf. A064397 (same for 2 primes), A072849 (4 primes), A166255 (70 primes), A166261 (120 primes).

Sequence in context: A076722 A322288 A337739 * A088944 A335000 A352806

Adjacent sequences: A076302 A076303 A076304 * A076306 A076307 A076308

KEYWORD

nonn

AUTHOR

Zak Seidov, Oct 05 2002

EXTENSIONS

Corrected by Ray Chandler, Sep 26 2006

STATUS

approved