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A281314 a(1) = 4; a(n) = smallest semiprime such that a(n) - a(n-1) is an odd prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

MAPLE

with(numtheory): P:=proc(q) local a, n; print(4); a:=4; for n from 5 to q do if bigomega(n)=2 then if isprime(n-a) and n-a>2 then a:=n; print(n); fi; fi; od; end: P(10^3); # Paolo P. Lava, Jan 25 2017

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

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Last modified July 1 14:35 EDT 2022. Contains 354973 sequences. (Running on oeis4.)