A053178 Numbers ending in 1 which are not prime.

1, 21, 51, 81, 91, 111, 121, 141, 161, 171, 201, 221, 231, 261, 291, 301, 321, 341, 351, 361, 371, 381, 391, 411, 441, 451, 471, 481, 501, 511, 531, 551, 561, 581, 591, 611, 621, 651, 671, 681, 711, 721, 731, 741, 771, 781, 791, 801, 831, 841, 851, 861, 871

Offset

1,2

Comments

Nonprime numbers of the form k*10+1. - Juri-Stepan Gerasimov, Oct 14 2009

Links

Table of n, a(n) for n=1..53.

Example

a(4) = 91 may look prime to some, but is composite.

Maple

remove(isprime, [10*j+1$j=0..99])[];  # Alois P. Heinz, Jan 21 2021

Prog

(PARI) isok(n) = ((n % 10) == 1) && (! isprime(n)) \\ Michel Marcus, Jul 26 2013
(Python)
from sympy import isprime
def aupto(lim): return [m for m in range(1, lim+1, 10) if not isprime(m)]
print(aupto(871)) # Michael S. Branicky, Jan 21 2021

Crossrefs

Cf. A002808, A017281, A153275.

Sequence in context: A153441 A357679 A235884 * A166150 A224334 A305002

Adjacent sequences: A053175 A053176 A053177 * A053179 A053180 A053181

Keyword

easy,nonn,base

Author

Enoch Haga, Feb 29 2000

Status

approved