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A263015 Integers n such that A007504(n) is the sum of 2 nonzero squares. 1
1, 2, 3, 4, 6, 7, 9, 11, 12, 14, 15, 21, 25, 29, 35, 55, 58, 59, 64, 71, 85, 89, 93, 94, 95, 100, 101, 102, 108, 112, 114, 116, 122, 124, 130, 131, 133, 135, 141, 146, 147, 151, 159, 162, 165, 170, 171, 172, 177, 178, 183, 190, 192, 193, 194, 204, 205, 206 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Integers n such that sum of the first n primes is the sum of 2 nonzero squares.

Initial values of corresponding sum of first n primes are 2, 5, 10, 17, 41, 58, 100, 160, 197 and 281.

LINKS

Table of n, a(n) for n=1..58.

EXAMPLE

a(3) = 3 because 2 + 3 + 5 = 3^2 + 1^2.

a(5) = 6 because 2 + 3 + 5 + 7 + 11 + 13 = 5^2 + 4^2.

a(6) = 7 because 2 + 3 + 5 + 7 + 11 + 13 + 17 = 7^2 + 3^2.

PROG

(PARI) a(n) = sum(k=1, n, prime(k));

is(n) = { for( i=1, #n=factor(n)~%4, n[1, i]==3 && n[2, i]%2 && return); n && ( vecmin(n[1, ])==1 || (n[1, 1]==2 && n[2, 1]%2)) }

for(n=1, 1e3, if(is((a(n))), print1(n, ", ")))

CROSSREFS

Cf. A000404, A007504.

Sequence in context: A257047 A192416 A026468 * A056176 A143831 A087072

Adjacent sequences:  A263012 A263013 A263014 * A263016 A263017 A263018

KEYWORD

nonn

AUTHOR

Altug Alkan, Nov 27 2015

STATUS

approved

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Last modified July 22 21:34 EDT 2019. Contains 325227 sequences. (Running on oeis4.)