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A242209 Semiprimes sp = p^2 + q^2 + r^2 where p, q and r are consecutive primes. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A007229 A297799 A204070 * A201244 A240263 A156661

Adjacent sequences:  A242206 A242207 A242208 * A242210 A242211 A242212

KEYWORD

nonn

AUTHOR

K. D. Bajpai, May 07 2014

STATUS

approved

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Last modified December 7 03:27 EST 2019. Contains 329836 sequences. (Running on oeis4.)