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A281960 Primes that are the sum of three consecutive odd semiprimes. 1
61, 79, 107, 139, 163, 191, 211, 263, 271, 373, 443, 617, 719, 733, 761, 971, 991, 1097, 1129, 1231, 1259, 1373, 1439, 1531, 1543, 1597, 1663, 1697, 1733, 1753, 1777, 1831, 2053, 2081, 2099, 2137, 2161, 2213, 2383, 2423, 2543, 2677, 2687, 2719, 2777, 2843, 2917 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 (1..3263 from K. D. Bajpai)

EXAMPLE

a(1) = 61 is a prime and 61 = 15 + 21 + 25; the sum of three consecutive odd semiprimes.

a(2) = 79 is a prime and 79 = 21 + 25 + 33; the sum of three consecutive odd semiprimes.

MATHEMATICA

Select[Total /@ Partition[Select[Range[2000], Plus @@ Last /@ FactorInteger[#] == 2 && OddQ[#] &], 3, 1], PrimeQ]

PROG

(PARI) list(lim)=my(v=List(), u=v, t, L=lim+10); forprime(p=3, L\3, forprime(q=3, min(p, L\p), listput(u, p*q))); u=Set(u); for(i=3, #u, if(isprime(t=u[i-2]+u[i-1]+u[i]), listput(v, t))); while((t=u[#u-1]+u[#u]+L++)<lim, if(bigomega(L)==2, u=concat(u, L); if(t>lim, break); if(isprime(t), listput(v, t)))); Vec(v) \\ Charles R Greathouse IV, Feb 03 2017

CROSSREFS

Cf. A000040, A001358, A034961, A034962, A281824.

Sequence in context: A328160 A118162 A217076 * A139931 A325076 A253232

Adjacent sequences:  A281957 A281958 A281959 * A281961 A281962 A281963

KEYWORD

nonn

AUTHOR

K. D. Bajpai, Feb 03 2017

STATUS

approved

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Last modified January 27 17:58 EST 2020. Contains 331296 sequences. (Running on oeis4.)