OFFSET
1,1
COMMENTS
Given p(i) the i-th prime number, the gap sequence of length n for prime p(i) is defined as: p(i+1)-p(i), p(i+2)-p(i+1), ..., p(i+n)-p(i+n-1). E.g., the length 3 gap sequence of 7 is [11-7, 13-11, 17-13] is [4, 2, 4].
EXAMPLE
For n = 5, the largest prime with a distinct gap sequence is 47. For all primes up to and including 47, the length 5 gap sequences are distinct, while the next prime, 53, has a gap sequence equal to 23, namely [6, 2, 6, 4, 2].
PROG
(Python)
s = set()
for p, g in ((w[0][0], tuple(r - q for q, r in w[1:])) for w in sliding_window(pairwise(primes()), n + 1)):
if g in s: return p
else: s.add(g)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Leo Vandriel, Feb 21 2024
STATUS
approved