A353814 - OEIS

A353814

a(n) = 1 if n is the sum of 2 distinct nonzero squares, 0 otherwise.

0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1

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OFFSET

COMMENTS

a(n) = 1 if n is divisible by at least one prime factor of form 4*k+1 and any prime factor 4*k+3 has even multiplicity, otherwise a(n) = 0.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..100000

Index entries for characteristic functions

FORMULA

a(n) = [A025441(n) > 0], where [ ] is the Iverson bracket.

a(n) >= A353813(n).

PROG

(PARI) A353814(n) = { my(f = factor(n), nb1 = 0, p, ep); for(i=1, #f~, p = f[i, 1]; ep = f[i, 2]; if(1==(p%4), nb1++, if(3==(p%4) && ep%2, return(0)))); (nb1>0); }; \\ After program in A353813 (originally from A230779)

CROSSREFS

Characteristic function of A004431.

Cf. A025441, A353813.

Sequence in context: A188009 A353812 A353813 * A144596 A188187 A341996

Adjacent sequences: A353811 A353812 A353813 * A353815 A353816 A353817

KEYWORD

nonn

AUTHOR

Antti Karttunen, May 15 2022

STATUS

approved