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A050244 Numbers n such that 2^n + 3^n is a semiprime. 4
3, 6, 7, 8, 10, 11, 12, 14, 16, 22, 32, 34, 38, 82, 83, 106, 128, 149, 218, 223, 334, 412, 436, 599, 647, 916, 1373, 4414, 7246, 8423, 10118, 10942, 15898 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Empirically, the smaller factor of 2^a(n) + 3^a(n) is a member of A294132 for all known terms. a(34) > 22000. - Hugo Pfoertner, Jul 29 2019

LINKS

Table of n, a(n) for n=1..33.

EXAMPLE

a(1)=3 because 2^3+3^3 = 5 * 7

a(2)=6 because 2^6+3^6 = 13 * 61

a(3)=7 because 2^7+3^7 = 5 * 463

a(4)=8 because 2^8+3^8 = 17 * 401

a(5)=10 because 2^10+3^10 = 13 * 4621

a(6)=11 because 2^11+3^11 = 5 * 35839

a(7)=12 because 2^12+3^12 = 97 * 5521

a(8)=14 because 2^14+3^14 = 13 * 369181

a(9)=16 because 2^16+3^16 = 3041 * 14177

a(10)=22 because 2^22+3^22 = 13 * 2414250301

a(11)=32 because 2^32+3^32 = 1153 * 1607133116929

a(12)=34 because 2^34+3^34 = 13 * 1282861452271981

a(13)=38 because 2^38+3^38 = 13 * 103911691734684541

a(14)=82 because 2^82+3^82 = 13 * 102329189594547549657540565413396038701

a(15)=83 because 2^83+3^83 = 5 * 798167678837469920188160718521149336927

a(16)=106 because 2^106+3^106 = 13 * 28900785585664327723593061693364968422740414514061

a(17)=128 because 2^128+3^128 = 257 * 45876204582640401445607833244277975113391731388650867226881

a(18)=149 because 2^149+3^149 = 5 * 24665899002341798194980052306171212216360861465143461865961807325057879

CROSSREFS

Cf. A001358, A007689, A082101, A294132.

Sequence in context: A168114 A220656 A324143 * A295566 A266986 A047283

Adjacent sequences:  A050241 A050242 A050243 * A050245 A050246 A050247

KEYWORD

nonn,more,hard

AUTHOR

Hugo Pfoertner, May 08 2003

EXTENSIONS

Corrected and extended by Hugo Pfoertner, May 12 2003

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 30 2007

a(28)-a(32) from Sean A. Irvine, Nov 05 2009

a(33) from Hugo Pfoertner, Jul 29 2019

STATUS

approved

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Last modified August 4 01:48 EDT 2020. Contains 336201 sequences. (Running on oeis4.)