A336403 - OEIS

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A336403

Multiplicative closure of A045468: numbers which are the product of zero or more primes which are 1 or 4 mod 5.

1, 11, 19, 29, 31, 41, 59, 61, 71, 79, 89, 101, 109, 121, 131, 139, 149, 151, 179, 181, 191, 199, 209, 211, 229, 239, 241, 251, 269, 271, 281, 311, 319, 331, 341, 349, 359, 361, 379, 389, 401, 409, 419, 421, 431, 439, 449, 451, 461, 479, 491, 499, 509

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

The subsequence of A089270 which excludes terms divisible by 5.

LINKS

David Friend, Table of n, a(n) for n = 1..10000

David Friend, Fibonacci-Like Sequences and their Cassini Constants, Multiplication and Factorisation

FORMULA

Numbers of the form r^2 + 3*r*s + s^2 not divisible by 5, where r and s are relatively prime and r > s >= 0.

CROSSREFS

Cf. A031363 and its subset A089270 and its subset A038872 and its subset A045468.