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A320707
Indices of primes followed by a gap (distance to next larger prime) of 18.
2
99, 180, 205, 221, 274, 293, 326, 368, 416, 529, 539, 573, 597, 602, 607, 623, 635, 639, 677, 693, 725, 785, 811, 838, 844, 852, 855, 916, 937, 939, 942, 945, 968, 997, 1028, 1093, 1130, 1151, 1203, 1227, 1252, 1304, 1311, 1349, 1508, 1514, 1519, 1523, 1540, 1547, 1629, 1636, 1641, 1654, 1656
OFFSET
1,1
COMMENTS
Indices of the primes listed in A031936.
FORMULA
a(n) = A000720(A031936(n)).
A320707 = { i > 0 | prime(i+1) = prime(i) + 18 } = A001223^(-1)({18}).
MATHEMATICA
Select[Range[1700], Prime[#] + 18 == Prime[# + 1] &] (* Vincenzo Librandi, Mar 22 2019 *)
Flatten[Position[Differences[Prime[Range[2000]]], 18]] (* Harvey P. Dale, May 12 2022 *)
PROG
(PARI) A(N=100, g=18, p=2, i=primepi(p)-1, L=List())={forprime(q=1+p, , i++; if(p+g==p=q, listput(L, i); N--||break)); Vec(L)} \\ returns the list of first N terms of the sequence
(Magma) [n: n in [1..1700] | NthPrime(n+1) - NthPrime(n) eq 18]; // Vincenzo Librandi, Mar 22 2019
CROSSREFS
Equals A000720 o A031936.
Row 9 of A174349.
Indices of 18's in A001223.
Cf. A029707, A029709, A320701, A320702, ..., A320720 (analog for gaps 2, 4, 6, 8, ..., 44), A116493 (gap 70), A116496 (gap 100), A116497 (gap 200), A116495 (gap 210).
Sequence in context: A055164 A075815 A075814 * A235228 A157947 A097599
KEYWORD
nonn
AUTHOR
M. F. Hasler, Oct 19 2018
STATUS
approved