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A351693 a(n) is the least prime prime(k) for which A351692(k) = n, or 0 if there is no such prime. 2
2, 3, 29, 13, 47, 19, 31, 647, 101, 107, 181, 569, 109, 839, 199, 811, 283, 373, 97, 73, 151, 79, 229, 149, 103, 443, 401, 701, 167, 751, 1901, 347, 379, 197, 157, 227, 673, 193, 383, 277, 353, 991, 313, 359, 419, 337, 911, 461, 1319, 1279, 349, 757, 2957, 1747, 827, 631, 457, 1511, 1249, 1559, 1091 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
a(n) = prime(k) for the least k such that prime(k)+2*prime(k+j) and prime(k)+2*prime(k-j) are both prime for j = n but not both prime for j = 1 ... n-1.
LINKS
EXAMPLE
a(3) = 13 = prime(6) because A351692(6) = 3 and A351692(k) <> 3 for 1 <= k < 6.
MAPLE
nP:= 10000: Primes:= [seq(ithprime(i), i=1..nP)]: R:= 2: found:= true:
for n from 1 to 300 while found do
found:= false;
for k from n+1 to nP-n do
if isprime(Primes[k]+2*Primes[k-n]) and isprime(Primes[k]+2*Primes[k+n]) and
andmap(t -> not isprime(Primes[k]+2*Primes[k-t]) or not
isprime(Primes[k]+2*Primes[k+t]), [$1..n-1]) then
R:= R, Primes[k]; found:= true; break
fi
od od:
R;
PROG
(PARI) f(n) = for (k=1, n-1, my(p=prime(n)); if (isprime(p + 2*prime(n-k)) && isprime(p + 2*prime(n+k)), return(k))); return(0); \\ A351692
a(n) = my(k=1); while (f(k) != n, k++); prime(k); \\ Michel Marcus, May 11 2022
CROSSREFS
Sequence in context: A003017 A096580 A371024 * A324941 A028868 A081332
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, May 05 2022
STATUS
approved

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Last modified June 24 07:41 EDT 2024. Contains 373663 sequences. (Running on oeis4.)