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A113339 Integers n such that prime(n+1)-prime(n) is nonprime, squarefree. Except for the initial term of 1, the terms are k-semiprime for some k>=2. 1
1, 9, 11, 15, 16, 18, 21, 23, 30, 32, 34, 36, 37, 39, 40, 42, 51, 53, 54, 55, 56, 58, 61, 62, 66, 67, 68, 71, 73, 74, 76, 80, 82, 84, 86, 96, 100, 101, 102, 103, 105, 106, 107, 108, 110, 111, 115, 118, 119, 123, 125, 127, 129, 130, 133, 137, 138, 141, 145, 146, 150 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..61.

FORMULA

prime(n+1)-prime(n)=1 or p1*...*pk where p1, ..., pk are two or more distinct primes.

EXAMPLE

prime(69)-prime(68)=347-337=10=2*5.

MAPLE

L:=[]: for z to 1 do for k from 1 to 200 do p:=ithprime(k); q:=nextprime(p); x:=q-p; if not(isprime(x)) and issqrfree(x) then L:=[op(L), k] fi od od; L;

CROSSREFS

Cf. A000040, A000469, A001358.

Sequence in context: A212816 A183980 A101754 * A270190 A320701 A287340

Adjacent sequences:  A113336 A113337 A113338 * A113340 A113341 A113342

KEYWORD

easy,nonn

AUTHOR

Walter Kehowski, Jan 08 2006

STATUS

approved

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Last modified April 10 22:05 EDT 2021. Contains 342856 sequences. (Running on oeis4.)