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URL: https://oeis.org/A120941

⇱ A120941 - OEIS

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A120941
a(n)=k-n where prime(k) is the smallest prime greater than prime(n)*prime(n+1).
2
3, 5, 9, 18, 30, 42, 60, 77, 113, 145, 179, 229, 262, 293, 353, 430, 487, 545, 622, 671, 737, 826, 916, 1052, 1184, 1249, 1310, 1373, 1443, 1654, 1894, 2026, 2131, 2298, 2481, 2602, 2782, 2943, 3107, 3298, 3436, 3651, 3866, 3975, 4083, 4346, 4808, 5144
OFFSET
1,1
COMMENTS
Parity of A120941: 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, ....
LINKS
FORMULA
a(n) = A000720(A006094(n)) + 1 - n. - Robert Israel, Mar 21 2017
EXAMPLE
The product of the 4th prime number, 7 and the 5th prime, 11, is 77; the smallest prime greater than this is the 22nd prime, 79; therefore the 4th term of the sequence is 22-4 = 18.
MAPLE
f:= n -> numtheory:-pi(ithprime(n)*ithprime(n+1))+1-n:
map(f, [$1..100]); # Robert Israel, Mar 21 2017
MATHEMATICA
Table[PrimePi[Prime[n]Prime[n + 1]] - n + 1, {n, 48}] (* Zak Seidov, Aug 21 2006 *)
PROG
(PARI) for(n=1, 100, print1(primepi(prime(n)*prime(n + 1)) - n + 1, ", ")) \\ Indranil Ghosh, Mar 22 2017
(Python)
from sympy import prime, primepi
print([primepi(prime(n)*prime(n + 1)) - n + 1 for n in range(1, 100)]) # Indranil Ghosh, Mar 22 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Axel Harvey, Aug 18 2006
EXTENSIONS
More terms from Robert G. Wilson v, Aug 21 2006
STATUS
approved