A320708 Indices of primes followed by a gap (distance to next larger prime) of 20.

154, 259, 442, 480, 548, 753, 777, 783, 876, 971, 1035, 1066, 1095, 1106, 1147, 1254, 1277, 1302, 1337, 1345, 1355, 1381, 1396, 1400, 1423, 1438, 1562, 1592, 1613, 1662, 1669, 1808, 1955, 2016, 2043, 2081, 2116, 2129, 2147, 2226, 2302, 2307, 2387, 2517, 2547, 2563, 2694, 2724, 2745, 2755, 2766

Offset

1,1

Comments

Indices of the primes listed in A031938.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..10720

Index entries for primes, gaps between.

Formula

a(n) = A000720(A031938(n)).

A320708 = { i > 0 | prime(i+1) = prime(i) + 20 } = A001223^(-1)({20}).

Mathematica

Select[Range[3000], Prime[#] + 20 == Prime[# + 1] &] (* Vincenzo Librandi, Mar 22 2019 *)

Prog

(PARI) A(N=100, g=20, 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..3000] | NthPrime(n+1) - NthPrime(n) eq 20]; // Vincenzo Librandi, Mar 22 2019

Crossrefs

Equals A000720 o A031938.

Row 10 of A174349.

Subsequence of A107730 (prime(n+1) ends in same digit as prime(n)).

Indices of 20'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: A214475 A327775 A053243 * A261377 A256024 A239564

Adjacent sequences: A320705 A320706 A320707 * A320709 A320710 A320711

Keyword

nonn

Author

M. F. Hasler, Oct 19 2018

Status

approved