OFFSET
1,1
COMMENTS
Inspired by problem A1 on the 2017 William Lowell Putnam Mathematical Competition.
Every positive integer greater than one will appear, except the multiples of 5.
For k > 2, the number of terms in row k is at least the sum of the number of terms in rows k-1 and k-2.
3 shows up for the first time no later than row 104.
LINKS
Jeremy F. Alm, Table of n, a(n) for n = 1..236
Jeremy F. Alm, First 10 rows
EXAMPLE
First few rows are
2;
49;
7, 2916;
54, 144, 8532241;
12, 2921, 3481, 22201, 72799221804516;
59, 149, 289, 8532246, 8561476, 12152196, 493106436, 299726695343845803536039441;
17, 2926, 3486, 4096, 22206, 23716, 86436, 72799221804521, 72799307127001, 73298956913361, 147675989144401, 243153962155686481, 28087103045340200593045577229687766576786428563667986916;
MATHEMATICA
NestList[Complement[DeleteDuplicates@ Join[# /. s_ /; IntegerQ@ Sqrt@ s :> Sqrt@ s, # /. k_ :> (k + 5)^2], #] &, {2}, 6] // Flatten (* Michael De Vlieger, Dec 06 2017 *)
PROG
(PARI) lista(nn) = my(row = [2], all = row); for (n=1, nn, row = concat(apply(x->(x+5)^2, row), apply(x->sqrtint(x), select(issquare, row))); all = concat(all, vecsort(row, , 8)); ); all; \\ Michel Marcus, Oct 16 2023
CROSSREFS
KEYWORD
nonn,tabf
AUTHOR
Jeremy F. Alm, Dec 05 2017
STATUS
approved