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A045698 Number of ways n can be written as the sum of two squares of primes. 7
0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 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, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

a(A214879(n)) = 0; a(A045636(n)) > 0; a(A214723(n)) = 1; a(A214511(n)) = n and a(m) < n for m < A214511(n). - Reinhard Zumkeller, Jul 29 2012

The smallest value of n such that a(n) = 2 is 338. (This helps distinguish it from the characteristic function of A045636.) - Wesley Ivan Hurt, Jun 13 2013

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

Index entries for sequences related to sums of squares

EXAMPLE

For example, a(29) = 1 because 29 = 2^2 + 5^2. a(3) = 0 because there is no way to write 3 as sum of two squares of primes.

PROG

(Haskell)

a045698 n = length $ filter (\x -> x > 0 && a010051' x == 1) $

map (a037213 . (n -)) $

takeWhile (<= div n 2) a001248_list

-- Reinhard Zumkeller, Jul 29 2012

(PARI) a(n)=my(s=0, q); forprime(p=2, sqrtint(n\2), if(issquare(n-p^2, &q)&&isprime(q), s++)); s \\ Charles R Greathouse IV, Jun 04 2014

CROSSREFS

Cf. A001248, A010051, A037213.

Sequence in context: A025461 A169674 A324053 * A106197 A011722 A276404

Adjacent sequences:  A045695 A045696 A045697 * A045699 A045700 A045701

KEYWORD

easy,nonn

AUTHOR

Felice Russo

EXTENSIONS

More terms from Erich Friedman

STATUS

approved

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Last modified June 14 12:04 EDT 2021. Contains 345025 sequences. (Running on oeis4.)