A033176 Threes and ones.

31, 31331, 313313331, 31331333133331, 31331333133331333331, 313313331333313333313333331, 31331333133331333331333333133333331, 31331333133331333331333333133333331333333331, 313313331333313333313333331333333313333333313333333331

Offset

1,1

Comments

a(n) is prime for n = 1 and n = 10, and no other n <= 230. - Robert Israel, Jun 17 2025

References

F. Smarandache, Properties of numbers, University of Craiova, 1973.

Links

Table of n, a(n) for n=1..9.

Formula

a(n) has increasing groups of 31, 331, ..., 33...31 (n times 3) concatenated.

Maple

a:= proc(n) option remember; `if`(n=0, 0, parse(cat(a(n-1), 3$n, 1))) end:
seq(a(n), n=1..10);  # Alois P. Heinz, Jun 17 2025

Crossrefs

Sequence in context: A263585 A176349 A262716 * A263163 A188956 A218142

Adjacent sequences: A033173 A033174 A033175 * A033177 A033178 A033179

Keyword

nonn,easy,base,less

Author

Jan Jensen (dorul(AT)post6.tele.dk)

Extensions

More terms from Erich Friedman.

Status

approved