OFFSET
1,1
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..10000
Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems: invphi.gp, Oct. 2005.
Jeppe Stig Nielsen, List of numbers with divisor sum k, k<=10000.
EXAMPLE
a(1) = 18, because 2*18 = 36 is the first occurrence of a row of 5 consecutive even numbers, all of which are in A000203. 36 = sigma(22), 38 = sigma(37), 40 = sigma(27), 42 = sigma(20) = sigma(26) = sigma(41), 44 = sigma(43);
a(2) = 78: 2*78 = 156 = sigma(99) = sigma(125), 158 = sigma(157), 160 = sigma(133), 162 = sigma(106), 164 = sigma(163);
See Jeppe Stig Nielsen's list for more examples.
PROG
(PARI) a342560(nterms) = {my(N=vector(5, i, invsigmaNum(2*i)), n=0, k=10, j=4); while(n<=nterms, if(vecmin(N)>0, print1((k-8)/2, ", "); n++); k+=2; N[1+(j++)%5] = invsigmaNum(k))};
a342560(49) \\ see Alekseyev link for invsigmaNum()
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, May 11 2021
STATUS
approved