A242209 Semiprimes sp = p^2 + q^2 + r^2 where p, q and r are consecutive primes.

38, 339, 579, 1731, 5739, 8499, 32259, 133851, 145779, 163851, 207579, 222531, 235779, 260187, 308019, 323619, 366819, 469731, 550491, 644979, 684699, 743091, 926427, 1003539, 1242939, 1743531, 1808259, 1852107, 1909059, 2075091, 2585571, 4226979, 5358291

Offset

1,1

Comments

Subsequence of A133529.

All the terms in the sequence, except a(1), are divisible by 3.

Links

K. D. Bajpai, Table of n, a(n) for n = 1..5100

Example

a(1) = 38 = 2^2 + 3^2 + 5^2 = 2*19 is semiprime.
a(2) = 339 = 7^2 + 11^2 + 13^2 = 3*113 is semiprime.

Maple

with(numtheory): A242209:= proc()local k ; k:=(ithprime(x)^2+ithprime(x+1)^2+ithprime(x+2)^2); if bigomega(k)=2 then RETURN (k); fi; end: seq(A242209 (), x=1..500);

Mathematica

Select[Total[#^2]&/@Partition[Prime[Range[300]], 3, 1], PrimeOmega[#]==2&] (* Harvey P. Dale, Nov 05 2015 *)

Prog

(PARI) for(k=1, 500, sp=prime(k)^2+prime(k+1)^2+prime(k+2)^2; if(bigomega(sp)==2, print1(sp, ", "))) \\ Colin Barker, May 07 2014

Crossrefs

Cf. A001358, A133529, A216432.

Sequence in context: A367968 A297799 A204070 * A201244 A240263 A156661

Adjacent sequences: A242206 A242207 A242208 * A242210 A242211 A242212

Keyword

nonn

Author

K. D. Bajpai, May 07 2014

Status

approved