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A079260 Characteristic function of primes of form 4n+1 (1 if n is prime of form 4n+1, 0 otherwise). 10
0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Let M(n) denote the n X n matrix m(i,j)=0 if n divides ij-1, m(i,j) = 1 otherwise then det(M(n))=-1 if and only if n =2 or if n is prime ==1 (mod 4).

a(A002144(n)) = 1; a(A137409(n)) = 0. [From Reinhard Zumkeller, Oct 11 2008]

a(n) * A151763(n) = a(n).

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Index entries for characteristic functions

MATHEMATICA

Table[If[PrimeQ[n]&&IntegerQ[(n-1)/4], 1, 0], {n, 120}] (* Harvey P. Dale, Jul 14 2015 *)

PROG

(PARI) { a(n)=if(n%4==1, isprime(n)) }; vector(100, n, a(n))

(Haskell)

a079260 n = fromEnum $ n `mod` 4 == 1 && a010051 n == 1

-- Reinhard Zumkeller, Oct 06 2011

CROSSREFS

Cf. A002144, A079261.

Cf. A066339 (partial sums).

Sequence in context: A011666 A011669 A023971 * A025457 A219463 A286688

Adjacent sequences:  A079257 A079258 A079259 * A079261 A079262 A079263

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Feb 04 2003

STATUS

approved

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Last modified October 19 16:17 EDT 2019. Contains 328223 sequences. (Running on oeis4.)