A049201 If n is not composite, a(n) = n followed by 1; if n is composite, a(n) = concatenation of prime factors of n.

1, 11, 21, 31, 22, 51, 23, 71, 222, 33, 25, 111, 223, 131, 27, 35, 2222, 171, 233, 191, 225, 37, 211, 231, 2223, 55, 213, 333, 227, 291, 235, 311, 22222, 311, 217, 57, 2233, 371, 219, 313, 2225, 411, 237, 431, 2211, 335, 223, 471, 22223, 77, 255, 317, 2213

Offset

0,2

Links

Table of n, a(n) for n=0..52.

Prog

(Python)
from sympy import factorint
def a(n):
    if n == 0: return 1
    f = factorint(n)
    if n == 1 or sum(f.values()) == 1: return int(str(n)+'1')
    return int("".join(str(p)*e for p, e in f.items()))
print([a(n) for n in range(53)]) # Michael S. Branicky, Jul 21 2021

Crossrefs

Cf. A049121, A037274.

Sequence in context: A109686 A077522 A308232 * A068633 A225297 A123849

Adjacent sequences: A049198 A049199 A049200 * A049202 A049203 A049204

Keyword

nonn,base,easy

Author

N. J. A. Sloane

Extensions

More terms from Michel ten Voorde

a(22) onward corrected by Sean A. Irvine, Jul 21 2021

Status

approved