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

1,1

Comments

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).

Links

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

Mathematica

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 *)

Crossrefs

Cf. A001358, A017558.

Sequence in context: A023488 A115585 A099980 * A004630 A073497 A244941

Adjacent sequences: A281311 A281312 A281313 * A281315 A281316 A281317

Keyword

nonn

Author

Zak Seidov, Jan 25 2017

Status

approved