A017558 -id:A017558 - cp's OEIS frontend

A281314 a(1) = 4; a(n) = smallest semiprime such that a(n) - a(n-1) is an odd prime.

4, 9, 14, 21, 26, 33, 38, 49, 62, 65, 82, 85, 122, 129, 134, 141, 146, 159, 166, 169, 206, 209, 214, 217, 254, 259, 262, 265, 278, 289, 302, 305, 334, 339, 346, 365, 382, 393, 398, 403, 422, 427, 446, 451, 454, 471, 478, 481, 542, 545

Offset: 1

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Zak Seidov, Jan 25 2017

nonn

a(n) >= A175587(n).

First differences: 5, 5, 7, 5, 7, 5, 11, 13, 3, 17, 3, 37, 7, 5, 7, 5, 13, 7, 3, 37, 3, 5, 3, 37, 5, 3, 3, 13, 11, 13, 3, 29, 5, 7, 19, 17, 11, 5, 5, 19, 5, 19, 5, 3, 17, 7, 3, 61, 3 (all odd primes).

Zak Seidov, Table of n, a(n) for n = 1..1000

Cf. A001358, A017558.

NestList[(p = 3; While[2 != PrimeOmega[q = # + p], p = NextPrime[p]]; q) &, 4, 50]
nxt[n_]:=Module[{k=n+1},While[PrimeOmega[k]!=2||!PrimeQ[k-n]||EvenQ[k-n],k++];k]; NestList[nxt,4,50] (* Harvey P. Dale, Feb 14 2019 *)

cp's OEIS Frontend

A281314 a(1) = 4; a(n) = smallest semiprime such that a(n) - a(n-1) is an odd prime.

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