A173656 - OEIS

A173656

Primes p such that p^2 divides P(p), where P = Perrin sequence A001608.

521, 190699

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

OFFSET

1,1

COMMENTS

It is not known if this sequence is infinite.

The squares are in A013998.

No other terms below 10^10. - Max Alekseyev, Aug 27 2023

LINKS

Table of n, a(n) for n=1..2.

G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 521

Wikipedia, Perrin number

EXAMPLE

521 is in the sequence since its square 271441 is the factor of A001608(521).

MATHEMATICA

lst = {}; a = 3; b = 0; c = 2; Do[P = b + a; If[PrimeQ[n] && Divisible[P, n^2], AppendTo[lst, n]]; a = b; b = c; c = P, {n, 3, 2*10^5}]; lst

lst = {}; PowerMod2[mat_, n_, m_] := Mod[Fold[Mod[If[#2 == 1, #1.#1.mat, #1.#1], m] &, mat, Rest@IntegerDigits[n, 2]], m]; LinearRecurrence2[coeffs_, init_, n_, m_] := Mod[First@PowerMod2[Append[RotateRight /@ Most@IdentityMatrix@Length[coeffs], coeffs], n, m].init, m] /; n >= Length[coeffs]; Do[n = Power[p, 2]; If[PrimeQ[p] && LinearRecurrence2[{1, 1, 0}, {3, 0, 2}, n, n] == 0, AppendTo[lst, p]], {p, 1, 2*10^5, 2}]; lst

PROG

(PARI)

/* Assuming b13998 containing second column of b013998.txt */

A013998 = readvec(b13998);

for (k=1, #A013998, if (issquare(A013998[k])==1, print(k, " ", A013998[k])));

/* Hugo Pfoertner, Sep 01 2017 */

CROSSREFS

Cf. A001608, A013998.

Sequence in context: A167734 A122715 A153180 * A015291 A028484 A057699

Adjacent sequences: A173653 A173654 A173655 * A173657 A173658 A173659

KEYWORD

bref,hard,more,nonn

AUTHOR

Arkadiusz Wesolowski, Aug 15 2012

STATUS

approved