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A264665 Integers n such that A002110(n) + 2 is the sum of 2 nonzero squares. 0
2, 3, 4, 5, 6, 11, 15, 33, 49, 50, 52, 53, 54, 57, 60, 61, 64, 68 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Integers n such that A006862(n) + 1 is the sum of 2 nonzero squares.

LINKS

Table of n, a(n) for n=1..18.

EXAMPLE

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

a(2) = 3 because 2*3*5 + 2 = 4^2 + 4^2.

a(3) = 4 because 2*3*5*7 + 2 = 14^2 + 4^2.

MATHEMATICA

Rest@ Select[Range@ 36, SquaresR[2, Product[Prime@ k, {k, #}] + 2] > 0 &] (* Michael De Vlieger, Nov 23 2015 *)

PROG

(PARI) a(n) = prod(k=1, n, prime(k)) + 2;

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, 1e5, if(is(a(n)), print1(n, ", ")))

CROSSREFS

Cf. A000404, A002110, A006862.

Sequence in context: A157420 A221471 A058243 * A264995 A060733 A283563

Adjacent sequences:  A264662 A264663 A264664 * A264666 A264667 A264668

KEYWORD

nonn,more

AUTHOR

Altug Alkan, Nov 20 2015

STATUS

approved

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Last modified February 23 21:23 EST 2018. Contains 299588 sequences. (Running on oeis4.)