A269840 Lesser of twin primes where both are the sum of 3 nonzero squares.

17, 41, 59, 107, 137, 179, 227, 281, 347, 419, 521, 569, 617, 641, 659, 809, 827, 857, 881, 1019, 1049, 1091, 1289, 1427, 1451, 1481, 1619, 1667, 1697, 1721, 1787, 1931, 2027, 2081, 2129, 2267, 2339, 2657, 2729, 2801, 2969, 3251, 3257, 3299, 3329, 3371, 3467, 3539

Offset

1,1

Links

Chai Wah Wu, Table of n, a(n) for n = 1..10000

Example

17 is a term because 17 = 2^2 + 2^2 + 3^2 and 19 = 1^2 + 3^2 + 3^2.
41 is a term because 41 = 3^2 + 4^2 + 4^2 and 43 = 3^2 + 3^2 + 5^2.
59 is a term because 59 = 3^2 + 5^2 + 5^2 and 61 = 3^2 + 4^2 + 6^2.

Prog

(PARI) isA000408(n) = my(a, b) ; a=1 ; while(a^2+1<n, b=1 ; while(b<=a && a^2+b^2<n, if(issquare(n-a^2-b^2), return(1) ) ; b++ ; ) ; a++ ; ) ; return(0) ;
t(n, p=3) = { while( p+2 < (p=nextprime( p+1 )) || n-->0, ); p-2}
for(n=1, 1e2, if(isA000408(t(n)) && isA000408(t(n)+2), print1(t(n), ", ")));

Crossrefs

Cf. A000408, A001359, A085317.

Sequence in context: A104043 A076330 A087658 * A237659 A350052 A078655

Adjacent sequences: A269837 A269838 A269839 * A269841 A269842 A269843

Keyword

nonn

Author

Altug Alkan, Mar 13 2016

Status

approved