A259980 Numbers that are 1+prime and have 4 proper divisors.

12, 18, 20, 32, 44, 68, 98, 164, 212, 242, 284, 332, 338, 524, 548, 578, 692, 788, 908, 1052, 1124, 1172, 1532, 1724, 1868, 2012, 2084, 2252, 2348, 2372, 2468, 2708, 2732, 2804, 2972, 3188, 3308, 3362, 3548, 3644, 3698, 3908, 3932, 4052, 4244, 4364, 4604, 4652

Offset

1,1

Links

Lars Blomberg, Table of n, a(n) for n = 1..10000

R. P. Boas & N. J. A. Sloane, Correspondence, 1974

Example

12 is 1+11, and has the proper divisors 2, 3, 4, 6.

Mathematica

Select[Prime@ Range@ 630 + 1, DivisorSigma[0, #] == 6 &] (* Michael De Vlieger, Jul 13 2015 *)

Prog

(PARI)  main(size)={my(v=vector(size), i, t); t=1; for(i=1, size, until(length(divisors(prime(t)+1))-2==4, t++); v[i]=prime(t)+1; t++); return(v); } /* Anders Hellström, Jul 13 2015 */

Crossrefs

Cf. A008864.

Sequence in context: A181487 A091191 A357696 * A257719 A071927 A362052

Adjacent sequences: A259977 A259978 A259979 * A259981 A259982 A259983

Keyword

nonn,easy

Author

N. J. A. Sloane, Jul 12 2015, following a suggestion from R. P. Boas, May 19 1974

Extensions

More terms from Lars Blomberg, Jul 13 2015

Status

approved