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A085417 Take prime[n] and continue adding n,n+1,..., n+a(n)-1 until one reaches a prime. 4
1, 1, 3, 1, 3, 1, 3, 9, 3, 5, 3, 5, 3, 12, 4, 9, 3, 1, 3, 4, 3, 1, 4, 1, 7, 1, 7, 5, 3, 4, 3, 1, 3, 1, 3, 8, 3, 9, 7, 5, 4, 1, 8, 12, 4, 4, 15, 1, 8, 21, 3, 5, 24, 9, 12, 8, 3, 4, 3, 9, 11, 4, 3, 5, 48, 1, 7, 33, 3, 1, 3, 1, 15, 12, 3, 5, 8, 5, 3, 36, 19, 1, 3, 5, 11, 5, 12, 5, 4, 4, 3, 1, 3, 5, 3, 1, 15, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Primes obtained are in A085418. See also A085415, A085416.
No terms == 2 (mod 4). - Robert Israel, Mar 24 2023
LINKS
EXAMPLE
a(3)=3 because prime[3]=5 and 5+(3+4+5)=17= is a prime A085418(3).
MAPLE
f:= proc(n) local m, k, x;
m:= ithprime(n) - (n-1)*n/2;
for k from n do
x:= k*(k+1)/2 + m;
if isprime(x) then return k+1-n fi
od;
end proc:
map(f, [$1..100]); # Robert Israel, Mar 24 2023
CROSSREFS
Sequence in context: A370719 A057024 A023892 * A201662 A274473 A280526
KEYWORD
easy,nonn
AUTHOR
Zak Seidov, Jun 30 2003
STATUS
approved

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Last modified April 19 19:02 EDT 2024. Contains 371798 sequences. (Running on oeis4.)