

A335667


a(n) is the smallest even number k such that k1 and k+1 are both nalmost primes.


1



4, 34, 274, 2276, 8126, 184876, 446876, 18671876, 95234374, 1144976876, 6018359374, 281025390626, 2068291015624, 6254345703124
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OFFSET

1,1


COMMENTS

10^13 < a(15) <= 181171630859374.  Giovanni Resta, Jun 21 2020


LINKS

Table of n, a(n) for n=1..14.
David A. Corneth, Upper bounds on a(n) for n = 1..37 where values with * are proven values


EXAMPLE

a(1) = 4 since 4  1 and 4 + 1 are both primes.
a(2) = 34 since 34  1 = 33 = 3*11 and 34 + 1 = 35 = 5*7 are both semiprimes.
a(3) = 274 since 274  1 = 273 = 3*7*13 and 274 + 1 = 275 = 5^2 * 11 are both 3almost primes.


MATHEMATICA

m = 8; v = Table[0, {m}]; c = 0; o1 = 1; n = 4; While[c < m, o2 = PrimeOmega[n + 1]; If[o1 == o2 && v[[o1]] == 0, c++; v[[o1]] = n]; o1 = o2; n += 2]; v


CROSSREFS

Cf. A001222, A088077, A115186, A154704.
Sequence in context: A198687 A116430 A216239 * A201684 A155628 A036352
Adjacent sequences: A335664 A335665 A335666 * A335668 A335669 A335670


KEYWORD

nonn,more


AUTHOR

Zak Seidov and Amiram Eldar, Jun 17 2020


EXTENSIONS

a(12)a(14) from Giovanni Resta, Jun 21 2020


STATUS

approved



