A391433 a(n) is the greatest prime that starts a sequence of two or more consecutive primes whose sum is A050936(n).

2, 3, 2, 5, 3, 2, 7, 5, 11, 3, 2, 13, 7, 17, 3, 11, 19, 7, 13, 23, 5, 3, 2, 17, 29, 7, 31, 19, 13, 3, 2, 37, 23, 41, 17, 43, 5, 29, 3, 47, 13, 19, 31, 53, 17, 59, 37, 5, 3, 61, 2, 41, 13, 67, 19, 43, 71, 7, 73, 5, 17, 3, 47, 2, 23, 79, 37, 13, 83, 53, 19, 29, 41, 89, 59, 5, 3, 17, 97, 61, 43, 101

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

a(14) = 17 because A050936(14) = 36 is the sum of two or more consecutive primes in two ways, 17 + 19 and 5 + 7 + 11 + 13, and 17 is the greatest starting prime of these.

Maple

N:= 1000: # for terms of A050936 up to N
P:= select(isprime, [2, seq(i, i=3..N, 2)]):
SP:= ListTools:-PartialSums([0, op(P)]): nSP:= nops(SP):
S:= {}:
for i from nSP-2 to 1 by -1 do
  for j from i+2 to nSP do
    s:= SP[j]-SP[i];
    if s > N then break fi;
    if not member(s, S) then
       S:= S union {s};
       R[s]:= P[i];
    fi
od od:
S:= sort(convert(S, list)):
[seq(R[S[i]], i=1..nops(S))];

Crossrefs

Cf. A050936, A084143, A390497.

Sequence in context: A104887 A064886 A390497 * A029600 A169616 A344448

Adjacent sequences: A391430 A391431 A391432 * A391434 A391435 A391436

Keyword

nonn,look

Author

Will Gosnell and Robert Israel, Dec 09 2025

Status

approved