1,1

Runs of semiprimes of the same parity: {4, 6}, {9}, {10, 14}, {15, 21}, {22}, {25}, {26}, {33}, {34}, {35}, {38}, {39}, {46}, {49, 51, 55, 57}, {58, 62}, {65, 69}, {74}, {77}, {82}, {85}, {86}, {87, 91, 93}, {94}, ...

a(12) > 2*10^14.

Table of n, a(n) for n=1..11.

a(1) = 22 since it is the first occurrence of a single even semiprime;

a(2) = 4 since 4 is the first of two consecutive even semiprimes in the sequence of semiprimes;

a(3) = 454 since it is the first of three consecutive even semiprimes in the sequence of semiprimes; etc.

SplitBy[ Select[ Range@ 100, PrimeOmega@# == 2 &], Mod[#, 2] &] (* to view the runs of semiprimes of the same parity *)

Cf. A001358, A304457, A304458.

Sequence in context: A018817 A040472 A139335 * A040469 A040468 A317740

Adjacent sequences: A304453 A304454 A304455 * A304457 A304458 A304459

nonn,more

Zak Seidov, Silvester Resnik and Robert G. Wilson v, May 12 2018

approved