login
A268494
Indices n of "late birds" (a(n)<a(k) for all k>n) in A268630 (= a(n)^2+a(n+1) is prime).
4
0, 2, 4, 12, 13, 14, 21, 44, 69, 76, 107, 109, 114, 127, 204, 214, 246, 249, 298, 317, 394, 402, 420, 440, 442, 477, 504, 508, 533, 550, 552, 610, 632, 647, 656, 682, 743, 745, 801, 808, 925, 943, 952, 954, 961, 966, 980, 1010, 1050, 1089, 1112, 1162, 1167, 1200, 1229, 1233, 1244, 1389, 1401, 1415, 1423, 1432, 1462
OFFSET
0,2
COMMENTS
See A268495 for the corresponding values. We use offset 0 here because the first term has a special status (it's not really "late") and also because all related sequences (A268630 and A268494 - A268497) have a(0)=0 and omitting this term yields the corresponding "positive integer" variant.
Assuming that A268630 is a permutation of the nonnegative integers N (as conjectured), the characterization given in the name is equivalent to say that a(n) equals the least number not occurring earlier. The sequence defined that way is finite if and only if A268630 is not a permutation of N.
LINKS
PROG
(PARI) show(n, a=0, u=[a-1])={for(n=1, n, a==u[1]+1&&print1(n-1", "); u=setunion(u, [a]); while(#u>1&&u[2]==u[1]+1, u=u[^1]); for(k=u[1]+1, 9e9, !setsearch(u, k) && isprime(a*a+k) && (a=k) && break))}
CROSSREFS
Sequence in context: A358502 A141668 A087796 * A306851 A316634 A039587
KEYWORD
nonn
AUTHOR
M. F. Hasler, Feb 09 2016
STATUS
approved