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A219697 Primes neighboring a 7-smooth number. 2
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 71, 73, 79, 83, 89, 97, 101, 107, 109, 113, 127, 139, 149, 151, 163, 167, 179, 181, 191, 193, 197, 199, 211, 223, 239, 241, 251, 257, 269, 271, 281, 293, 337, 349, 359, 379, 383, 401, 419 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This is to the 7-smooth numbers A002473 as A219528 is to the 3-smooth numbers A003586 and as A219669 is to the 5-smooth numbers A051037. The first primes NOT within one of a 7-smooth number are 103, 131, 137, 157, 173, ...

LINKS

Table of n, a(n) for n=1..57.

FORMULA

Primes INTERSECTION {2^h 3^i 5^j 7^k +/-1 for h,i,j,k >= 0}.

MATHEMATICA

mx = 2^10; t7 = Select[Sort[Flatten[Table[2^i * 3^j * 5^k * 7^l, {i, 0, Log[2, mx]}, {j, 0, Log[3, mx]}, {k, 0, Log[5, mx]}, {l, 0, Log[7, mx]}]]], # <= mx &]; Union[Select[t7 + 1, PrimeQ], Select[t7 - 1, PrimeQ]] (* T. D. Noe, Nov 26 2012 *)

CROSSREFS

Cf. A000040, A002473, A051037, A080194, A219528.

Sequence in context: A234960 A118850 A322443 * A078668 A038614 A171047

Adjacent sequences:  A219694 A219695 A219696 * A219698 A219699 A219700

KEYWORD

nonn,easy

AUTHOR

Jonathan Vos Post, Nov 25 2012

STATUS

approved

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Last modified July 5 07:06 EDT 2020. Contains 335460 sequences. (Running on oeis4.)