A082448 Add 1, multiply by 1, add 2, multiply by 2, etc.; start with 4.

4, 5, 5, 7, 14, 17, 51, 55, 220, 225, 1125, 1131, 6786, 6793, 47551, 47559, 380472, 380481, 3424329, 3424339, 34243390, 34243401, 376677411, 376677423, 4520129076, 4520129089, 58761678157, 58761678171, 822663494394, 822663494409, 12339952416135, 12339952416151, 197439238658416

Offset: 0

Author

N. J. A. Sloane, based on a suggestion of Nick MacDonald, Apr 25 2003

Keywords

• nonn
• easy

Links

• Nick Hobson, Python program for this sequence

Crossrefs

Cf. A019461 (same, but start with 0), A019463 (start with 1), A019460 (start with 2), A019462 (start with 3).

Cf. A082458, A019464 .. A019466 (similar, but first multiply, then add).

Programs

Mathematica

k = 0; NestList[(k++; {Last@# + k, k(k + Last@#)}) &, {4}, 16] // Flatten

PARI

a=4; for(n=1,150,print(a,","); b=if(n%2-1,a*ceil(n/2),a+ceil(n/2)); a=b)

PARI

A082448(n,a=4)={for(i=2,n+1,if(bittest(i,0),a*=i\2,a+=i\2));a} \\ M. F. Hasler, Feb 25 2018

Formula

For n>=2, a(2n)=floor((2e+4)*n!)-n-2, a(2n+1)=floor((2e+4)*n!)-1.

Extensions

More terms from Benoit Cloitre, Apr 26 2003

Edited by M. F. Hasler, Feb 25 2018